There is provided an opening/closing device for an upper unit case, including a pair of guide members formed of lower and upper guide members provided on lower and upper unit cases respectively, at least one of the lower and upper guide member being configured to be swingable in an up and down direction; a movable body which is connected movably to the lower and upper guide members and which has a rotary body installed in the movable body while being fitted rollably with respect to the lower and lower guide members; and a regulating mechanism which regulates swinging amount in the up and down direction of the at least one guide member configured to be swingable in the up and down direction.