To make a lid hardly become an obstacle when the lid is opened by allowing automatic opening and closing in an automatic opening/closing device of the lid such as a toilet lid.

Automatic opening/closing of the folding lid 23 can be realized with a simple constitution by guiding a front lid 1 to the position where its upper face lies on nearly the same plane as the upper face of a rear lid 2 when the rear lid 2 is rotated to the closing direction (counterclockwise direction), and by providing a wire 5 for guiding the front lid 1 to the position where the front lid lies on top of the rear lid 2 when the rear lid 2 is rotated to the opening direction (clockwise direction).