Abstract: Two positioning devices (4, 5) are horizontally spaced apart from two clamping devices (6, 6) at a predetermined interval. Each of the positioning devices (4, 5) includes a positioning hole (23) provided by opening a work pallet (2), a plug portion (27) projecting from a clamp pallet (1), and an intermediate member (30) vertically movably supported by the plug portion (27). The intermediate member (30) is urged upwards by a coned disk spring (31) and has a tapered surface (33) which makes a tapering engagement with the positioning hole (23). The clamping device (6) fixes the work pallet (2) to the clamp pallet (1).