A driving force transmission apparatus (2) includes: a housing (20); an inner shaft (23); a main clutch (3) including first outer and inner clutch plates (31, 32); a cam mechanism (4) generating pressing force for pressing the main clutch by relatively rotating a pair of cam members (41, 42); and an electromagnetic clutch mechanism (5) including an armature (50) and applying rotation force to the cam mechanism (4) for relatively rotating the cam members (41, 42) through energization of an electromagnetic coil (53). An end face (212a) facing the armature (50) is formed in the inner peripheral spline portion (210) between a first region (210a) engaged with the first outer clutch plate (31) and a second region (210b) engaged with the armature (50). Movement of the armature toward the first region (210a) is regulated by contact of the armature with the end face (212a).