Power transmission device having electromagnetic clutch

A power transmission device having an electromagnetic clutch, wherein the electromagnetic clutch has a solenoid coil, a coil housing disposed surrounding the solenoid coil, an armature plate disposed facing the side of the coil housing, and a clutch mechanism, the armature plate being linked to a rotation input member, and the rotation input member and a rotation output member being engaged and disengaged by the clutch mechanism,

• the current flowing to the solenoid coil is controlled so as to control the clamping of the armature plate to the coil housing, and the clamping force acting on the armature plate is made to act on the clutch mechanism via a cam mechanism so as to control the engagement of the clutch mechanism, and
• a first rotational backlash amount BLm occurring between the rotation input member and the rotation output member in a rotation transmission system in which the clutch mechanism is interposed in a state in which the clutch mechanism is engaged, and a second rotational backlash amount BLp occurring between the rotation input member and the rotation output member in a rotation transmission system in which the cam mechanism is interposed in a state in which the cam mechanism is fixed and the armature plate is clamped to the coil housing, are set such that BLm>BLp.