Provided is a phase-variable device for an engine, which can perform the transmission of a torque between a clutch case and a rotary drum by making use of an oil film. The engine phase-variable device causes relative rotations between an outer cylinder portion (10) and an inner cylinder portion (20) by moving an intermediate member (30) axially, thereby changing the opening/closing timings of an intake valve or an exhaust valve. The engine phase-variable device comprises an annular rotary drum (44) connected to the intermediate member (30), and an electromagnetic clutch (42) for controlling a braking force on the rotary drum (44) in accordance with the running state of the engine. The electromagnetic clutch (42) includes an annular clutch case (60) arranged to face the rotary drum (44), and an electromagnetic coil (62) for generating, when powered, a braking force on the rotary drum (44). Grooves (66 and 67) are formed in the end face (63a) of the inner circumference wall (63) and in the end face (64a) of the outer circumference wall (64) of the clutch case (60), so that the transmission of a torque between the rotary drum (44) and the clutch case (60) is performed through the grooves (66 and 67) and the oil film formed therearound.