The present invention provides a transmission mechanism that enables a reduction in motion transmission error between an input-shaft side and an output-shaft side. A transmission mechanism is provided with a cam, a plurality of pins arranged along a side surface of the cam, guide plates in which a plurality of guide holes are provided, and gears capable of engaging the pins. In conjunction with rotation of the cam, each pin is guided by the corresponding guide hole and moves along the cam and the gears, thereby causing the guide plates or gears to rotate relative to the cam. The plurality of pins are divided into a plurality of groups, and the pins in each group are coupled in series, but are not coupled to the pins in the other groups.