The present invention provides a marine reversing gear assembly, wherein a manual directional control valve 7a and an electromagnetic directional control valve 7b for a forward/reverse directional control valve 7 for hydraulic oil supply circuit 10 have a common structure of an oil line joint surface for the hydraulic oil supply circuit 10 for friction discs of a forward clutch 2f and a reverse clutch 2a, and the forward/reverse directional control valve 7 for the hydraulic oil supply circuit 10 can be changed to either the manual directional control valve 7a or the electromagnetic directional control valve 7b by exchanging spools 7c or 7e of the manual directional control valve 7a or the electromagnetic directional control valve 7b. Therefore, the operational manner of the forward/reverse directional control valve for the hydraulic oil supply line of a marine reversing gear assembly can be changed quite easily between the manual directional control valve and the electromagnetic directional control valve.