An overhead door is provided with a pair of stays and respective stay holding tension springs arranged such that, when the door is closed, they are expanded only less than twice of their length they have when the door is opened so that they are not subjected to excessive loads and hence can have a prolong service life. Each of the stays is rotatably fitted to the inner surface of a corresponding lateral wall of a cabinet main body by way of a rotary shaft and have its front end pivotably secured to the door at a position close to the lower edge of the door. A pair of slide rail assemblies, each comprising an outer rail and an inner rail 9b, are arranged such that the outer rails are fitted longitudinally in parallel with each other on the inner surface of the door and the upper end of each of the inner rails is pivotably secured to the front edge of the roof board of the cabinet main body. Each of the stay holding tension springs are soarranged that each of them is hooked at an end to a position located upward and forward relative to the corresponding rotary shaft on the inner surface of the related lateral wall of the cabinet main body and at the opposite end to a middle point of the corresponding stay. Thus, the outer rails and the door are urged upward relative to the inner rails by the stay holding tension springs so that the door may be opened lightly and the torque applied to the door when the door is closed is alleviated by the stay holding tension springs.