A catcher (2) comprises a catcher stopper (21), a holding body (22) for holding a striker body (1), and a biasing body (23) for them. When the catcher stopper (21) is projected by the biasing body (23), the holding body (22) is located at the forward position in a non-holding state. When the holding body (22) is located at the backward position in a holding state, the catcher stopper (21) is retracted. An engaging hole (402) for the catcher stopper (21) is formed in a recess (MB). A biasing force is stored in the biasing body (3) when the catcher (2) is located at the reference position where the catcher stopper (21) is engaged with the engaging hole (402). When the movable body (M) is moved forward to the self-propelling start position, the striker body (1) is advanced into the holding body (22) of the catcher (2) at the reference position.