A heat treatment method for a silicon wafer, comprising: supporting a silicon wafer on a three-points supporting device, and heat-treating the silicon wafer, supported on the three-points supporting device, in a heat treatment furnace, the three-points supporting device comprising three support arms (31, 32, 33) protruding from a support frame towards a center so as to form an intervening spacing with each other; the support frame having a rectangular-like shape whose one side is open in plan view, where the support frame has a first support arm provided at a side opposite to the opening of the support frame, and a second and a third support arms (32, 33) provided at the other sides of the support frame, and upper surfaces of the three support arms (31, 32, 33) being placed in the same plane, each of the support arms (31, 32, 33) has a support projection (41, 42, 43) projecting upwards from the upper surface of the support arm, on which a silicon wafer can be mounted, the method further comprises positioning all the support projections (41, 42, 43) on a same circle so that all the support projections (41, 42, 43) are positioned within a region where a radial distance (r) from the center is defined by 85 to 99.5% of the radius of the silicon wafer, characterized in that each of the support arms (31,32,33) has a plurality of fixing holes (51,52,53) provided at predetermined positions on the support arms, and the support projection (41,42,43) can be fixed at one of the fixing holes (51,52,53), the support arms (31, 32, 33) are arranged so as to form an angle of 120° with each other about the center of the support frame, and all the support positions of the silicon wafer are arranged forming angles of 120° about the center. supporting a silicon wafer on a three-points supporting device, and heat-treating the silicon wafer, supported on the three-points supporting device, in a heat treatment furnace, the three-points supporting device comprising three support arms (31, 32, 33) protruding from a support frame towards a center so as to form an intervening spacing with each other; the support frame having a rectangular-like shape whose one side is open in plan view, where the support frame has a first support arm provided at a side opposite to the opening of the support frame, and a second and a third support arms (32, 33) provided at the other sides of the support frame, and upper surfaces of the three support arms (31, 32, 33) being placed in the same plane, each of the support arms (31, 32, 33) has a support projection (41, 42, 43) projecting upwards from the upper surface of the support arm, on which a silicon wafer can be mounted, the method further comprises positioning all the support projections (41, 42, 43) on a same circle so that all the support projections (41, 42, 43) are positioned within a region where a radial distance (r) from the center is defined by 85 to 99.5% of the radius of the silicon wafer, characterized in that each of the support arms (31,32,33) has a plurality of fixing holes (51,52,53) provided at predetermined positions on the support arms, and the support projection (41,42,43) can be fixed at one of the fixing holes (51,52,53), the support arms (31, 32, 33) are arranged so as to form an angle of 120° with each other about the center of the support frame, and all the support positions of the silicon wafer are arranged forming angles of 120° about the center.