A sheet supply device includes a sheet supply tray, a guide fence for restricting sheets along a sheet width direction, a slider block that is slidable along the sheet width direction and supports the guide fence in an upright state, a slide shaft that is inserted into a through hole formed in the slider block and guides sliding of the slider block, and a guide fence lock mechanism including a restriction member on which a hole is formed and that is attached to the slider block swingably (the slide shaft is inserted into the hole). The guide fence lock mechanism restricts sliding of the slider block by holding the restriction member in a lock state where an inner circumferential edge of the hole is pushed onto an outer circumference of the slide shaft, and allows sliding of the slider block when the restriction member is swung to cancel the lock state.