Provided is an opening/closing body opening/closing device capable of effectively preventing water such as rainwater flowing down from an opening/closing body carried by a carrier plate from adhering to a guide rail. The opening/closing body opening/closing device includes a carrier plate that carries an opening/closing body, and a guide rail that guides movement of the carrier plate in a lifting and lowering direction of the opening/closing body. The carrier plate includes, at an upper end portion, a water holding section that holds water reaching the upper end portion of the carrier plate from above. The water holding section includes a water receiving section that faces upward and receives the reaching water, and an outflow preventing section provided with a preventing surface that faces the water receiving section side and prevents the water from flowing out to the guide rail.