In a paper sheet bundling apparatus for a paper sheet processing system, a thermally fusible bundling tape is wound round a paper sheet stack, and the trailing end of the tape is thermally bonded to a portion of the tape wound round the stack by a heating means. The bonding operation is effected on a heat receiving member interposed between the paper sheet stack and the tape wound thereround. The heat receiving member has a back side, outwardly curved contact surface, against which one edge portion of the paper sheet stack is urged and curved along it by a pressing lever in an initial stage of the bundling operation commencing with the rotation of a rotary body.