A wheel house unit structure is provided which has a wheel house including a curved surface portion, a circular cylindrical suspension tower provided at the curved surface portion, at the vehicle front side, of the wheel house, and a reinforcement member connected to the curved surface portion of the wheel house and to an outer circumference of the suspension tower. The reinforcement member has a ridge which connects the curved surface portion and the outer circumference of the suspension tower in a front-and-rear direction of the vehicle, and forms a closed cross section structure with the curved surface portion of the wheel house and the outer circumference of the suspension tower.