To provide a locking device for a cover which makes it possible to open and close a hatch cover tending to be large in size from either the right or left side of a small-sized planing boat and, besides, can prevent impairment of the beauty of the small-sized planing boat.

A locking device L is provided on the lower side of the rear end part 10b of a cover 10 and operation members 13 for releasing the locking of this locking device L are provided at the right and left positions near a handle, while constitution is so made that a state of engagement of the cover 10 can be canceled by operating either or both of these operation members 13 and that the cover 10 can be opened by operating the operation member 13 from either the starboard or port of an operating seat.