To provide an opening and closing device capable of automatically locking an operation muntin for opening and closing operation of an opening and closing body in a closing position.

A winding shaft 10 is provided in an upper part of an opening part 8, and the operation muntin 13 is attached to a tip of a screen 11 wound around the winding shaft 10. A pair of guide rails 14 guiding elevation movement of both end parts of the operation muntin 13 are provided on both sides of the opening part 8. An oscillating operation lever 31, a rod 38 moving in the axial direction in the interlocking relationship with the oscillation of the operation lever 31, and an oscillating lock lever 45 which holds the rod 38 at a retraction position and whose tip part protruded downward from a lower face of the operation muntin 13 are incorporated into the inside of the operation muntin 13. When the operation muntin 13 is pulled down to the closing position where it is substantially overlapped on a receive face 2a, the lock lever 45 is oscillated up to a lock release position due to the contact with the receive face 2a, the rod 38 is moved outward by spring of a spring 37, and a tip of the rod 38 is inserted into an engaging hole 54 provided in the guide rail 14 to lock the operation muntin 13 in a fully closed position.