A manufacturing method of a reactor device with a plurality of leg portion iron cores (1, 10), and yoke section iron cores which are arranged at both ends of the leg portion iron cores (1, 10), wherein: each of the leg portion iron cores (1, 10) is formed of an amorphous metal wound iron core which has an insertion hole that penetrates through the centre, and a slit formed along a radial direction; and each of the yoke section iron cores is formed of an amorphous metal wound iron core which has a substantially oval shape and a long hole communicated with the insertion holes of the leg portion iron cores (1, 10), wherein: in the manufacturing method, each of the leg portion iron cores (1, 10) is subjected to processes of forming the slit and annealing while having the wound iron core (1, 10) fixed to two iron core fixture jigs (5, 6); wherein the manufacturing method further comprises, for each of the leg portion iron cores (1, 10): removing one of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10); then tightening an outer circumference of the wound iron core (1, 10) with an insulator band or an insulator tape for fixation; and then removing the other of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10). each of the leg portion iron cores (1, 10) is formed of an amorphous metal wound iron core which has an insertion hole that penetrates through the centre, and a slit formed along a radial direction; and each of the yoke section iron cores is formed of an amorphous metal wound iron core which has a substantially oval shape and a long hole communicated with the insertion holes of the leg portion iron cores (1, 10), wherein: in the manufacturing method, each of the leg portion iron cores (1, 10) is subjected to processes of forming the slit and annealing while having the wound iron core (1, 10) fixed to two iron core fixture jigs (5, 6); wherein the manufacturing method further comprises, for each of the leg portion iron cores (1, 10): removing one of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10); then tightening an outer circumference of the wound iron core (1, 10) with an insulator band or an insulator tape for fixation; and then removing the other of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10). in the manufacturing method, each of the leg portion iron cores (1, 10) is subjected to processes of forming the slit and annealing while having the wound iron core (1, 10) fixed to two iron core fixture jigs (5, 6); wherein the manufacturing method further comprises, for each of the leg portion iron cores (1, 10): removing one of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10); then tightening an outer circumference of the wound iron core (1, 10) with an insulator band or an insulator tape for fixation; and then removing the other of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10). removing one of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10); then tightening an outer circumference of the wound iron core (1, 10) with an insulator band or an insulator tape for fixation; and then removing the other of the two iron core fixture jigs (5, 6) from the wound iron core (1, 10).