PURPOSE: To improve the operationability by enlarging a lock click to release locking and allowing drive rotation of shaft while blocking reverse rotation, thereby selecting the operating position and angle of lever freely and rotating the drive shaft continually through reciprocation of lever within relatively small rotary angle.

CONSTITUTION: In a car seat lifter, a rotary lock mechanism 8 is mounted at one end of a drive shaft 4 for receiving the operating force required for moving the lifter frame up and down through a rotary link. Said mechanism 8 is provided with a pair of drive clicks 19 to be enlarged and disengaged from a ratchet 24 when retreating the lever rod 22 against a a spring 18 by means of a knob 17. Upon disengagement of the clicks 19, the lever 14 can rotate together with the housing 13 in random direction. Under reciprocation of lever 14 while engaging the drive click 19 and ratchet 24, reverse rotation of drive shaft 4 is prevented through function between a pair of lock clicks 32 and ratchet 34.