A bicycle electric power unit supplies electric power to a bicycle motor unit having a power source, a power source controller, a power source voltage detector, a first power source switch and a second power source switch. The power source controller turns off the first power source switch when the power source voltage detector detects a voltage of a specific value or less. The first power source switch supplies electric power to the power source controller when the power source is on and blocks the electric power to the power source controller when the power source is off. The first power source switch is turned off by the power source controller when the power source is on. The second power source switch is disposed between the power source and the motor unit. The second power source is turned on and off by the power source controller.