A sheet loader for loading a folded sheet bundle provided from a sheet bundle provider with a folded edge of the folded sheet bundle in the lead, including: a folded edge support configured to support the folded edge of the folded sheet bundle provided from the sheet bundle provider, the folded edge support movable back and forth in a direction declined from a side near the sheet bundle provider, and an undersurface support configured to support an undersurface of the folded sheet bundle so that the folded edge is lower than a trailing edge of the folded sheet bundle.