To provide a screw installation structure that makes the height of a planar member adjustable relative to a supporting plate through a screwing degree of the screw installed on the planar member and that dispenses with a tapping operation as well as reducing cost.

The peripheral part 8 of a circular through hole 7 prepared in a planar member 1 is formed in a tapered shape, and is divided into a first and second peripheral parts 8a, 8b sectioned halfway around each. The thickness t1 of the peripheral parts 8a, 8b is thinner than one pitch t2 of the thread 4 of the screw 3. The screw 3 is engaged with the thread 4 at the first peripheral part 8a. At the second peripheral part 8b, the side face 7a of the through hole 7 is brought into contact with the ridge 4a of the thread 4, with the screw held in inclination to the through hole 7 and screwed into it, so that the tip end 3a of the screw 3 comes into contact with the reference face 2a on the supporting plate 2.