A hinge mechanism for use with a cover for opening and closing a hole. The mechanism is designed to support the cover and enable the cover to rotate through an angle greater than 90.degree. between an opened position and a closed position. The mechanism comprises an axle to be secured to the chamber, a support member having a first part rotatably supported by the axle and a second part spaced from the first part, a rotary member to be secured to the cover, the rotary member rotatably supported by the second part of the support member and capable of rotating around the support member when the cover is rotated, and a rotation-transmitting mechanism supported by the support member, connecting the rotary member to the axle to allow the support member to rotate in a first direction around the axle when the rotary member is rotated in a second direction opposite to the first direction. Once the hinge mechanism is incorporated in the vacuum-process apparatus, with the axle and the rotary member secured to the chamber and the cover, respectively, the support member can rotate in the direction opposite to the direction the cover is rotated around the rotary member between the closed position and the open position.