tumblers for a client lock although only one of the tumblers 31 is shown for clarity of illustration it should be understood that a plurality of tumblers are normally successively stacked preferably with spacers interposed between the respective pairs of adjacent tumblers each of the tumblers 31 is provided in its side opposed to the fence 23 with a gate 32 into which fence 23 can enter and provided along an end opposite to said gate 32 with engaging notches 34 in the form of saw teeth the engaging notches 34 can engage and disengage an associated one of two diametrically opposed projections formed on a supporting shaft 71 which is in turn stationarily mounted in the lock housing 11 when one of these engaging notches 34 engages the associated projection on supporting shaft 71 the tumblers 31 may be rotated or rocked around said one of the engaging notches 34 there is provided adjacent a middle and upper portion of the tumblers 31 a spring normally biasing tumblers 31 downward so that the tumblers 31 are biased to rotate counterclockwise so far as the engaging notches 34 are engaged with the supporting shaft 71 there is provided between the gate 32 and the engaging notches 34 a fan shaped or curved opening 33 through which a conversion shaft 35 extends the conversion shaft 35 is rotatably supported in the lock housing 11 and so formed as to be rotatable by a prescribed conversion key from the rear side of the lock housing 11 further the conversion shaft 35 includes an eccentric portion 36 adapted to bear against the right side concave surface of the opening 33 formed in the tumblers 31 when the conversion shaft 35 assumes its fixed position.