The invention provides MOCVD reactors, with which, while deposited films are uniformized in thickness, film deposition efficiency can be improved. An MOCVD reactor (1) is furnished with a susceptor (5) and a duct (11). The susceptor (5) has a carrying surface for heating and carrying substrates (20). The duct (11) is for conducting reaction gas G to the substrates (20). The susceptor 5 is rotatable with the carrying surface fronting on the duct (11) interior. The duct (11) has channels (11 b ) and (11 c ), which merge on the duct end upstream of Point A4 . The height of the duct (11) running along the reaction gas G flow direction monotonically diminishes heading toward the duct downstream end from Point P1 to Point P2, stays constant from Point P2 to Point P3 , and monotonically diminishes heading downstream from Point P3 . Point P1 lies upstream of Point A4 , while Point P3 lies on the susceptor 5.