A lock with a locking function adapted to be actuated after the insertion of a coin, in which the coin drops into a supported position in the bolt which is displaceable by key actuation, the edge of the coin releasing the bolt for the locking displacement by disengaging a pawl. The supported position is established by a resting point on the bolt side and a second resting point, the distance between the two resting points being variable as a function of the closing movement. One of the resting points is formed by the free, eccentrically shaped end of a rotary projection which is seated in a bolt-side lever which upon locking movement passes against spring action into a position which is at a greater distance from the bolt resting point. The rotary projection forms an attack surface, facing the rear wall of the lock, for a conversion tool.