A position detecting device includes: a position indicator including a
signal generator configured to generate an alternating-current
signal, a plurality of electrodes, a switch circuit configured to supply the alternating-current
signal to selected one(s) of the electrodes based on a predetermined
electrode-selection pattern, and a pattern information
transmitter configured to transmit pattern information indicating a set predetermined pattern. A tablet includes electrodes disposed in a flat surface manner, a signal
position detector configured to obtain a coordinate position of the alternating-current signal transmitted from said selected one(s) of the electrodes on a tablet surface based on distribution of a
signal level induced in each of the tablet electrodes by the alternating-current signal, a pattern information
receiver, and a rotation angle
calculator configured to calculate a rotation angle of the position indicator about a
perpendicular direction to the tablet surface based on a plurality of coordinate positions obtained according to the received pattern information.