To provide an opening/closing device and a bag storage vessel capable of retaining a condition where an opening part of a rubbish bag or the like without providing a special mechanism and excellent in operability at a time of use.

A rubbish loading opening 7 and a slidable slider 12 are provided on an inner lid 5 installed on an opening part of a vessel main body storing the rubbish bag. Both ends of a pair of open close members 21, 21 having elasticity in parallel are rotatably connected, a connecting part on one end side is attached to the inner lid 5 and a connecting part on another end side is attached to the slider 12 to run through the rubbish loading opening 7. The connecting part on one end side of the pair of open close members 21, 21 is pressed and moved toward the connecting part on another end side against elastic repulsion force which both connecting parts have by movement of the slider 12 to enable operation to an open condition where middles of extension of the pair of open close members 21, 21 is bent in directions to separate each other. After that, the pair of open close members 21, 21 automatically restore to a close condition where both members are set in parallel by self elastic restoring force.