To effectively prevent the mis-shift from a parking position of a transmission by providing a gear device and a rotation prevention device engageable for preventing the rotation of this gear device and also an interlocking member engaged with the rotation prevention device.

A part/lock mechanism 50 has an actuator 51 connected to a turning member 13 by a link mechanism 52. The actuator 51 is installed so as to actuate by taking out the hydraulic pressure in a transmission 53 and the hydraulic pressure is controlled by a solenoid valve 54 electrically connected to a shifter 120. The link mechanism 52 is composed of a toggle link constituted in T letter shape for pressing the turning member 13 to a holding position engaged with the notch 12 of a notch drum 11 and includes a rod 25 slidably attached with a sliding body 78. A spring 82 fitted to the rod 25 energizes the rod 25 to a stretch position, so that the turning member 13 is turned and a tooth 14 is engaged with the notch 12 to lock the turning member 13.