To easily manufacture the lock of the housed state and withdrawn state of a slide plate at a low cost by simply combining extremely few components, to surely and repeatedly slide and fix the slide plate without causing malfunctions, to withdraw it through one action at the time of use and to house it at the lower part of a top plate and a shelf so as not to be an obstacle in nonuse.

In this locking device of the slide plate in which the slide plate 5 is provided below a base plate 1, a locking hole 3 for the time of use and a locking hole 4 for the time of housing are perforated at the back surface part 2 of the base plate 1, a hanging metal fitting 6 is fixed to the appropriate part of the base plate back surface part of a device body and the hanging metal fitting 6 is provided with a slide rail 7. The slide plate 5 is arranged so as to be slid by using the slide rail 7 as a guide, an operator 8 is arranged through a bearing plate 9 on the back surface of the slide plate 5 and a locking part 12 is detached from the locking holes 3 and 4 by vertically swinging it with the shaft 10 of the operator 8 as a center.