PURPOSE: To eliminate need of complicated assembling and reassembling for facilitating completing a double backset lock by providing plural cams corresponding to plural backset values in a simple constitution.

CONSTITUTION: A front cam 30A and a back cam 30B are composed of two hub parts to be rotation-supported and engaged with two cam guide parts between two engagement halves of housing outer shells. Next, as either the front cam 30A or the back cam 30B is rotated, a bolting lock bar 20, that is a bolt 2, makes straight translation along an axis of a bolting actuation assembly to protrude or retract the bolt 2. As either cam is then rotated clockwise, the bolt 2 is retracted. In selecting a backset value, therefore, changing parts or reassembling the bolting assembly is not needed, but the backset value can be easily selected.