A four wheel drive transmission housing includes a transmission housing member, and a converter housing member including an engine mount portion on a first side of the converter housing; a transfer mount portion defining a first side joint surface on the first side; and a transmission housing mount portion defining a second side joint surface on a second side of the converter housing member. First and second reinforcing ribs are formed between the first side joint surface and the second side joint surface. The first reinforcing rib extends in a vertically extending first direction, from a rib connecting portion. The second reinforcing rib extends in a horizontally extending second direction from the rib connecting portion. The first and second reinforcing ribs are provided so as to surround a drive shaft to transmit driving power from the transmission mechanism to the transfer.