A sheet folding apparatus includes: a first sheet conveying unit; a second sheet conveying unit that is disposed downstream of the first sheet conveying unit; a folded part forming unit that forms a folded part on a sheet by nipping a turned-back portion formed on a part of the sheet between the first sheet conveying unit and the second sheet conveying unit; a second conveying path that bifurcates from the first conveying path and in which a sheet with the folded part is conveyed; and a pushing member that is movable between a pushing position at which the pushing member pushes the turned-back portion toward the folded part forming unit and a retracted position. The pushing member also serves as a changing unit that changes a direction of a leading end of the sheet that is conveyed in the first conveying path into a direction toward a second conveying path.