A driving unit that assists rider's pedal effort comprising: an electric motor for providing a driving force to assists rider's pedal effort; a crankshaft to which pedals (33,34) are to be connected; a crank rotation detector configured to detect rotation of the crankshaft; and an assist control stopping unit configured to stop assist by the electric motor in response to rotation of the crankshaft detected by the crank rotation detector, wherein the crank rotation detector is configured to put out a pulse signal in response to rotation of the crankshaft, and the assist control stopping unit is configured to stop assist control based on the pulse signal output from the crank rotation detector, the driving unit further comprises: a torque detector configured to detect a torque generated at the crankshaft; and a motor rotation detector configured to detect a rotation speed of the electric motor, wherein the assist control stopping unit comprises: a torque determination unit configured to determine whether the torque detected by the torque detector is equal to or less than a torque threshold; a motor rotation determination unit configured to determine whether the rotation speed of the electric motor detected by the motor rotation detector is equal to or more than a rotation speed threshold, characterized by a determination time interval setting unit configured to set a determination time interval in response to the rotation speed of the electric motor; a duration measuring unit configured to measure a duration in which the torque is determined as being not more than the torque threshold and the rotation speed is determined as being equal to or more than the rotation speed threshold and resets the measured duration to zero if the pulse signal is output from the crank rotation detector; and an assist stop determination unit configured to stop assist control if the duration measured by the duration measuring unit is more than the determination time interval set by the determination time interval setting unit. an electric motor for providing a driving force to assists rider's pedal effort; a crankshaft to which pedals (33,34) are to be connected; a crank rotation detector configured to detect rotation of the crankshaft; and an assist control stopping unit configured to stop assist by the electric motor in response to rotation of the crankshaft detected by the crank rotation detector, wherein the crank rotation detector is configured to put out a pulse signal in response to rotation of the crankshaft, and the assist control stopping unit is configured to stop assist control based on the pulse signal output from the crank rotation detector, the driving unit further comprises: a torque detector configured to detect a torque generated at the crankshaft; and a motor rotation detector configured to detect a rotation speed of the electric motor, wherein the assist control stopping unit comprises: a torque detector configured to detect a torque generated at the crankshaft; and a motor rotation detector configured to detect a rotation speed of the electric motor, wherein the assist control stopping unit comprises: a torque determination unit configured to determine whether the torque detected by the torque detector is equal to or less than a torque threshold; a motor rotation determination unit configured to determine whether the rotation speed of the electric motor detected by the motor rotation detector is equal to or more than a rotation speed threshold, characterized by a determination time interval setting unit configured to set a determination time interval in response to the rotation speed of the electric motor; a duration measuring unit configured to measure a duration in which the torque is determined as being not more than the torque threshold and the rotation speed is determined as being equal to or more than the rotation speed threshold and resets the measured duration to zero if the pulse signal is output from the crank rotation detector; and an assist stop determination unit configured to stop assist control if the duration measured by the duration measuring unit is more than the determination time interval set by the determination time interval setting unit.