An electric pump for supplying a hydrogen gas to a fuel cell includes a rotary shaft rotatably inserted through an electric motor, a transmitting member provided on one of an outer peripheral surface of the rotary shaft and an inner peripheral surface of the electric motor so as to be rotatable therewith, and a groove formed in the other of the outer peripheral surface of the rotary shaft and the inner peripheral surface of the electric motor for the transmitting member to be inserted therein. The groove transmits a rotary torque of the electric motor to the rotary shaft by contacting an inner surface of the groove and the transmitting member and has an opening width along a rotary direction of the rotary shaft which is larger than the width of the transmitting member. The groove and the transmitting member produce an impact torque when the electric pump is started.