An opening/closing device includes a fixed member, an opening/closing member, and a hinge device. The fixed member has inside wall sections and pin insertion holes. The opening/closing member has outside wall sections and pin supporting holes. The hinge device has a case that is inserted and held between the inside wall sections, pressing members that are disposed inside the case and are capable of rotating, a spring disposed between the pressing members, and pin members that are inserted through the pin supporting holes and the pin insertion holes and engage with the pressing members. The pin members are inserted through the pin supporting holes and the pin insertion holes from the outside of the outside wall sections.