Abstract: Provided is a workpiece positioning device that facilitates the replacement work of a positioning pin and does not require a mechanical mechanism for clamping a workpiece. This is a workpiece positioning device that positions a workpiece (W) by inserting a positioning pin (6) into a positioning hole (Wa) of the workpiece (W), wherein the workpiece positioning device comprises three locking members (5) that grip the positioning pin (6) in a protruding condition, and exert a magnetic attractive force, and three sliding members (3) that move each of the three locking members (5) forward and backward radially with respect to the positioning pin (6). The locking member (5) is formed in the shape of a cylindrical column, and grips the positioning pin (6) with an outer circumferential surface (5a) thereof and magnetically attracts the workpiece (W) with a top surface (5a) thereof. The magnetic attractive force of the locking member (5) is adjusted by excitation means.