Bicycles have been recognized for their advantages such as low environmental impact, health improvement, and maintenance of transportation function in times of disaster, and demand for bicycles is increasing as social conditions change. The pedaling of a conventional bicycle nowadays turns a crank to rotate the front gear, which is transmitted to the rear gear by a chain, and turns the rear axle to rotate the rear wheel. Since bicycles require human power to pedal, a structure that allows bicycles to be pedaled with a low load has been considered so that more people can easily use bicycles. This study developed a new bicycle power transmission system that enables bicycles to be pedaled with a low load without using gearbox or external power such as motor. In order to verify the effectiveness of the newly developed bicycle power transmission device, a prototype bicycle with the proposed device was fabricated and tested. Participants quantitatively evaluated the physical load with and without the device by pedaling the bicycle. The experimental results showed that the developed bicycle power transmission device can reduce the physical load.