A coin operated lock having a coin insertion aperture (3) permits a catch hook (5) to pivot when a coin (7) has been inserted through said aperture. This results in the displacement of an intermediate member (10) that includes two coin support means (17, 18). To enable the lock to be adjusted to operate with coins of different sizes, one support means (17) can be releasably fixed in an elongate aperture (20) with the aid of a screw (16), said aperture (20) being angled to the movement direction of the intermediate member. Adjustment of the support means to correspond to a coin of another size is effected from outside the lock with the aid of a screwdriver inserted through an elongate aperture (20) corresponding to the elongate aperture in the cover plate (2a) of the lock housing. One end position of the support device (17) in the elongate aperture (20) corresponds suitably to a coin of given size, e.g. a euro coin.