A fastening apparatus configured for fastening a plurality of workpieces (W1, W2), through which through holes (W10, W20) are respectively provided, using a fastener, wherein: an intermediate piece made of a carbon fiber-reinforced thermoplastic resin, which comprises a first head part and a shaft part formed integrally with the first head part and which extends in an axial direction, is used; the fastening apparatus comprising: a fastening device (1, 3) configured for heating only the shaft part in a noncontacting state and then applying pressure while the shaft part of the intermediate piece is inserted through the through holes (W10, W20) of the workpieces (W1, W2) and for forming a second head part on the intermediate piece integrally with the shaft part and opposing the first head part, thereby forming the fastener; and a determining device configured for determining whether the fastener has passed or failed; wherein: the fastening device (1, 3) comprises: a high-frequency induction coil, which is capable of inductively heating the shaft part thereby bringing the shaft part to a plastically deformable softened state, the high-frequency induction coil having a recessed part formed in a tip part thereof, and the high-frequency induction coil being capable of generating magnetic force lines that induce eddy currents in carbon fibers inside the shaft part of the intermediate piece received within the recessed part; a fastening die that is capable of forming the second head part from the heated shaft part; and a pressure-applying device that is capable of applying pressure to the fastening die; and the determining device configured for calculating a load curve defined by the time and the load during which pressure is applied and determines whether an amount of change per unit of time in the load curve after a reference load has been exceeded is within a range of a first reference value that is set in advance. an intermediate piece made of a carbon fiber-reinforced thermoplastic resin, which comprises a first head part and a shaft part formed integrally with the first head part and which extends in an axial direction, is used; the fastening apparatus comprising: a fastening device (1, 3) configured for heating only the shaft part in a noncontacting state and then applying pressure while the shaft part of the intermediate piece is inserted through the through holes (W10, W20) of the workpieces (W1, W2) and for forming a second head part on the intermediate piece integrally with the shaft part and opposing the first head part, thereby forming the fastener; and a determining device configured for determining whether the fastener has passed or failed; a fastening device (1, 3) configured for heating only the shaft part in a noncontacting state and then applying pressure while the shaft part of the intermediate piece is inserted through the through holes (W10, W20) of the workpieces (W1, W2) and for forming a second head part on the intermediate piece integrally with the shaft part and opposing the first head part, thereby forming the fastener; and a determining device configured for determining whether the fastener has passed or failed; the fastening device (1, 3) comprises: a high-frequency induction coil, which is capable of inductively heating the shaft part thereby bringing the shaft part to a plastically deformable softened state, the high-frequency induction coil having a recessed part formed in a tip part thereof, and the high-frequency induction coil being capable of generating magnetic force lines that induce eddy currents in carbon fibers inside the shaft part of the intermediate piece received within the recessed part; a fastening die that is capable of forming the second head part from the heated shaft part; and a pressure-applying device that is capable of applying pressure to the fastening die; and a high-frequency induction coil, which is capable of inductively heating the shaft part thereby bringing the shaft part to a plastically deformable softened state, the high-frequency induction coil having a recessed part formed in a tip part thereof, and the high-frequency induction coil being capable of generating magnetic force lines that induce eddy currents in carbon fibers inside the shaft part of the intermediate piece received within the recessed part; a fastening die that is capable of forming the second head part from the heated shaft part; and a pressure-applying device that is capable of applying pressure to the fastening die; and the determining device configured for calculating a load curve defined by the time and the load during which pressure is applied and determines whether an amount of change per unit of time in the load curve after a reference load has been exceeded is within a range of a first reference value that is set in advance.