The present invention provides a container opening/closing device for opening and closing a lid of a container. The container comprises a container body including an opening and the lid detachably attached to the opening. The device comprises an opening/closing mechanism including a holding portion for holding the lid and a pressing mechanism. The opening/closing mechanism opens and closes the opening by moving the holding portion between a closing position and an open position. The pressing mechanism presses a peripheral edge of the holding portion toward the container body when the opening/closing mechanism moves the lid from the open position to the closing position.