The invention relates to a sheet transport apparatus and an image recording apparatus. A sheet transport apparatus includes a first casing in which a transport path is formed; a transport unit which transports a sheet along the transport path; a second casing which is provided to be movable with respect to the first casing; a sheet support unit which is rotatably provided in the first casing at a position on a side to which the second casing is moved, the sheet support unit being changeable between a first state, a second state, and a third state and supporting the sheet at least in the third state; and an urging unit which urges the sheet support unit toward the first state within a range from the first state to the second state and which urges the sheet support unit toward the third state within a range from the second state to the third state.