To perform reliable positioning and storing corresponding to a fixed shape and a non-fixed shape size sheet as moving operability of a sheet guide is excellently kept.

In a sheet storage device formed that sheets 3 are stored in a sheet tray 1 and the storing position of the sheets 3 is regulated by the sheet guide 2, a guide holder 4 is provided to position and hold the sheet guide 2 on the sheet tray 1 side. A positioning pin 5 is protruded from either of the sheet guide 2 and the guide holder 4, and the positioning pin 5 is provided with a positioning part 5a and a non-positioning part 5b having a cross section smaller than that of the positioning part 5a. Meanwhile, a plurality of positioning holes 6 fitted in a positioning part 5a of the positioning pin 5 are formed in the other member. A communication passage 7 which has width narrower than that of the positioning hole 6 and in which a non-positioning part 5b of the positioning pin 5 is movable is formed between the positioning holes 6. Further, a slide pin sliding along a guide groove is provided together with a whirl stop part.