A sheet folding apparatus includes an adjuster which supports a stack of sheets stacked on an inclined surface of a sheet path and adjusts a position of the stack of sheets along the inclined surface, a stapler which staples the stack of sheets set at a stapling position, a folding unit which folds the stack of sheets set at a folding position, and a guide provided between the stapler and the folding unit. The stapler ejects a staple from a staple surface by sinking from the inclined surface. The folding unit includes folding rollers and a folding blade which inserts the stack of sheets into a nip between the folding rollers. The guide includes a loading surface offset from the staple surface and an uprising member which is disposed on a part of the loading surface to keep the stack of sheets symmetric with respect to the folding rollers.