Abstract: An apparatus for forming a snap ring groove in a clutch drum by pressing a lower die, an upper die, a workpiece supporting member, first sliding members and second sliding members, a workpiece receiving member fixed on a radially inner end of each first sliding member, and a punch fixed on an upper end of each upwardly bent portion in a radially inner end portion of each second sliding member. The first sliding members and the second sliding members are pushed radially inwards and outwards, respectively, via a cam mechanism by lowering the upper die. The cam mechanism is made of a first cam mechanism for driving the first sliding members and a second cam mechanism for driving the second sliding members. The first cam mechanism is arranged to push the first sliding members radially inwards, when lowering the upper die, with a radially outer end portion thereof operating as a point of action.