In a work pallet positioning and fixing device that positions a work pallet over a base member in the horizontal direction and in the vertical direction and fixes it thereto by pressing forces of clamp bolts, the base member is provided with first and second reference members for positioning, and a reference seating surface and, by making bolt head accommodation holes of bolt holes for four fitting bolts fitting flange portions of the reference members partially overlap with protruding engagement portions as seen in plan view, a plurality of tapered engagement surfaces on the external peripheries of the protruding engagement portions being segmented into four sections.