PURPOSE: To rotate a seat to a desired position by containing a control part to rotate the seat to a boarding position by way of rotating a motor by a driving part at the time of receiving a first signal and to return the seat to a driving position by way of rotating the motor by the driving part at the time of receiving a second signal.

CONSTITUTION: At the time of boarding from a boarding position on the left side, a passenger irradiates an infrared ray toward a light receiving part 24 installed on the boarding position on the left side. When a light receiving element 20a of the light receiving part 24 detects the infrared ray, a signal is output to a rotation judgement part 12 through an amplifying part 20b, and the rotation judgement part 12 judges that this signal is a signal from the light receiving part 24. Thereafter, the rotation judgement part 12 judges that the light receiving part 24 is installed on the boarding position on the left side and judges that it is the shortest to rotate this seat 60 to the left to rotate the seat to this position. Consequently, it is possible to direct a posture to a driving position by rotating the seat forward without using physical strength.