An actuator mechanism includes a attachment member fixed to a seat elevation adjuster and a controlling member placed between a driver member and the attachment member and can rotate together with an actuating lever. The driver member is located between the attachment member and a rotary member and fitted over a center shaft. There is formed a feed projection at one terminal portion of the driver member and its opposite terminal portion is placed face to face with a locking member. When the actuating lever is operated, the controlling member moves the driver member, which causes the locking member and the feed projection to engage with and disengage from the rotary member.