Control device (4) for a multi-
phase converter (20) having converter circuits (20a to 20c) of m (where m is an integer of at least 3) phases, each of which comprises a switching element (36a to 36c) and which are connected in parallel to one another, the control device (4) comprising: a controlled-
phase number control unit configured to increase the number of controlled phases of the converter circuits (20a to 20c) by increasing the number of switching elements (36a to 36c) on which on / off control is performed as a current value input to the multi-
phase converter (20) increases, and to control the multi-
phase converter (20) in n-phase drive where the number of controlled phases is n (where n is an integer less than m and at least 2 and is an integer that is not a divisor of m), or in m-phase drive where the number of controlled phases is m; a storage unit configured to store first and second patterns which are phase patterns in which on-times of the switching elements of m phases are defined; a selection unit configured to select the first or second pattern while the multiphase converter (20) has been stopped; an on / off
control unit configured to perform on / off control on the switching elements of the plurality of driven phases based on the phases set in the selected first or second pattern under a condition that a period and a duty ratio are substantially equal; and a prediction unit configured to predict a correlation value that correlates with a
time ratio that is, in a predetermined time, a ratio of a time for which the execution of a control in the m-phase drive is predicted to a time for which the execution of a control in the n-phase drive is predicted, wherein an absolute value of a difference between a maximum value of a
phase difference between two switching elements set to be sequentially turned on in the n-phase drive based on the second pattern and 360° / n is smaller than an absolute value of a difference between a maximum value of a
phase difference between two switching elements set to be sequentially turned on in the n-phase drive based on the first pattern and 360° / n, wherein the selection unit is configured to select the first pattern if the predicted correlation value indicates that the
time ratio is at least as large as a first threshold, and to select the second pattern if the predicted correlation value indicates that the
time ratio is smaller than a second threshold which is at most as large as the first threshold, wherein the on / off
control unit is arranged to stop the on / off control on the switching elements of (mn) phases in the n-phase drive based on the second pattern, wherein the switching elements are classified into a plurality of combinations such that each of the combinations is composed of three switching elements which are determined to be sequentially turned on in the m-phase drive based on the second pattern, wherein, when (mn)=1, the switching element of the (mn) phase at which the on / off control was stopped in the n-phase drive based on the second pattern is the switching element that is switched on between the switching element that is switched on first and the switching element that is switched on last, out of the three switching elements in a combination having a
phase difference that is the smallest among the plurality of combinations, the phase difference being a phase difference between the switching element that is switched on first and the switching element that is switched on last, and wherein, when (mn)≥2, the switching elements of (mn) phases at which the on / off control was stopped in the n-phase drive based on the second pattern are switching elements other than a combination of two switching elements set to be sequentially turned on in the m-phase drive based on the second pattern, and each turned on between the switching element that is turned on first and the switching element that is turned on last among the three switching elements in a corresponding one of (mn) combinations among the plurality of combinations, the (mn) combinations being selected in ascending order of the phase difference between the switching element that is turned on first and the switching element that is turned on last.