A cover opening/closing device prevents backlash when the cover is closed, by engaging the cover with a lock cam and urging the lock cam to be rotated into positions by a toggle spring. For this object, this device comprises a lock cam which is rotated about a rotational shaft provided in a main body, an operation lever which rotates the lock cam to open the cover, and a toggle spring which is designed to maintain the lock cam in urged states at the respective cover-opened and cover-closed positions. The lock cam can be kept urged in the cover-closed state.