A workpiece machining jig includes: a base member of an H cross-sectional shape integrally having two vertical flanges and a web having an interior hollow portion and extending horizontally to connect between the vertical flanges; first and second pallets fixed to the opposite surfaces of the web for placing thereon four workpieces, two workpieces on each of the pallets, in a horizontal posture. Each of the pallets has a pallet-side communication hole communicating to the hollow portion, and each of the flanges has a flange-side communication hole communicating to the hollow portion. The pallet-side communication hole of each of the pallets and the flange-side communication hole of a corresponding one of the flanges are interconnected by a tube extending in the hollow portion. Thus, four workpieces are machined concurrently using the single workpiece machining jig.