ADVANCING/RETREATING MOVEMENT DEVICE

An advancing/retreating movement mechanism of an advancing/retreating member includes: a lifter ; a coil spring ; a lock pin that limits the movement of the lifter ; a case that accommodates the lifter and the coil spring ; an advance/retreat position control mechanism that controls an advance position, a retreat position, and a reciprocating movement of the lifter ; and a receiving seat that receives the coil spring so that the lifter is biased. The receiving seat is arranged in a rearward position side of the lifter . An engaging part engaging the lock pin is arranged to the lifter . When the lifter moves to the retreat position, the engaging part moves to a rearward side beyond the receiving seat and moves to a position where the engaging part can be engaged with the lock pin . Therefore, the size of the advancing/retreating member in a protruding/withdrawing direction can be made small.