A device for casting a cylinder head of an internal combustion engine having a crankshaft and a plurality of cylinders (C1, C2, C3) respectively including a plurality of ports for air intake or exhaust, comprising a casting mold comprising an upper die, a lower die, and side dies (38a, 38b) that relatively approach and move away from each other so as to define an interior cavity that corresponds to the outer shape of the cylinder head, and a casting core supported in the cavity, and comprising a plurality of body parts (41, 44) having outer shapes that respectively correspond to the plurality of ports and a base part, wherein the lower die comprising a first surface (33a, 33b) that corresponds to an opening surface of the ports on a combustion chamber side and a second surface that faces a lower surface of the base part, the side dies (38a, 38b) comprise a third surface that faces the second surface, and the casting core is configured such that the body parts (41, 44) are supported in the cavity by distal ends (42a, 42b, 45a, 45b) of the body parts (41, 44) coming in contact with the first surface (33a, 33b), the lower surface of the base part coming in contact with the second surface, and an upper surface of the base part coming in contact with the third surface, characterized in that: the base part is formed integrally with the plurality of body parts (41, 44) at proximal end (43, 46) sides of the plurality of body parts (41, 44); at least two first engagement portions (331a, 331b) each having a contact surface (332a 1, 332a 2, 332b 1, 332b 2) that is substantially parallel to an axial direction of the crankshaft are formed on the first surface (33a, 33b); at least two second engagement portions (421a, 421b, 451a, 451b) loosely fitted to the first engagement portions (331a, 331b), respectively, and each having a contact surface (422a 1, 422a 2, 422b 1, 422b 2, 452a 1, 452a 2, 452b 1, 452b 2) that is substantially parallel to the axial direction of the crankshaft are formed at the distal ends (42a, 42b, 45a, 45b) of the body parts (41, 44); and the casting core is supported in the cavity in a state in which the contact surfaces (332a 1, 332a 2, 332b 1, 332b 2) of the first engagement portions (331a, 331b) and the contact surfaces (422a 1, 422a 2, 422b 1, 422b 2, 452a 1, 452a 2, 452b 1, 452b 2) of the second engagement portions (421a, 421b, 451a, 451b) are in contact with each other. the base part is formed integrally with the plurality of body parts (41, 44) at proximal end (43, 46) sides of the plurality of body parts (41, 44); at least two first engagement portions (331a, 331b) each having a contact surface (332a 1, 332a 2, 332b 1, 332b 2) that is substantially parallel to an axial direction of the crankshaft are formed on the first surface (33a, 33b); at least two second engagement portions (421a, 421b, 451a, 451b) loosely fitted to the first engagement portions (331a, 331b), respectively, and each having a contact surface (422a 1, 422a 2, 422b 1, 422b 2, 452a 1, 452a 2, 452b 1, 452b 2) that is substantially parallel to the axial direction of the crankshaft are formed at the distal ends (42a, 42b, 45a, 45b) of the body parts (41, 44); and the casting core is supported in the cavity in a state in which the contact surfaces (332a 1, 332a 2, 332b 1, 332b 2) of the first engagement portions (331a, 331b) and the contact surfaces (422a 1, 422a 2, 422b 1, 422b 2, 452a 1, 452a 2, 452b 1, 452b 2) of the second engagement portions (421a, 421b, 451a, 451b) are in contact with each other.