A hydraulic pressurizer system (30) comprises a drive source (an engine 2 and a motor generator 4), which drives a hybrid vehicle (1), a mechanical oil pump (20), which is driven by the drive source, an electrical motor (22), which is activated by a 12V battery (24), an electrical oil pump (21), which is driven by the electrical motor (22), and a control unit (15), which activates the electrical motor (22). The pressurizer further comprises a ratio-change mechanism (7), which is activated by hydraulic oil supplied by the mechanical oil pump (20) and by the electrical oil pump (21) to establish a speed change ratio, at which the rotational driving force of the drive source is transmitted to wheels (8) with a rotational speed change. For executing a control for stopping the drive source, the control unit (15) executes a cleaning operation, which operates the electrical oil pump (21) for a predetermined time before the stopping of the drive source.