PURPOSE: To provide an opening/closing device simple in structure and easily designed and constructed so as to open/close a shutter body along a suspension rail with a corner part regarding the opening/closing device for a laterally opened shutter with unit panels connected laterally and flexibly around a vertical shaft.

CONSTITUTION: An opening/closing device for a laterally opened shutter is provided with a shutter body 10 for closing an opening part 35, and a suspension rail 25 extended from the upper side of the opening part 35 to the upper side of a side wall 36 via a corner part 37. A driving pulley 42 and a driven pulley are disposed at both ends of the part, extended along the side wall 36, of the suspension rail 25, and a belt 44 wound around both pulleys is connected to the aftermost unit panel l of the shutter body 10. The corner part 37 of the suspension rail 25 is provided with a tie rail 38 having a guide groove 41 for guiding a suspended wheel.