To propose a hinge pin enabling attachment and detachment to/from a motor-driven opening / closing unit.

By making the hinge pin into a bendable structure, the attachment and detachment of the hinge pin to/from the motor-driven opening / closing unit are made possible. Also, by providing an insertion margin on a toilet lid receiving side hinge pin and a motor-driven opening / closing receiving side hinge pin mutually, the connection of the two hinge pins is strengthened and the power of the motor-driven opening / closing unit is surely transmitted to a toilet seat and a toilet lid.