There is provided a wheel motor device including a hydraulic motor unit. The hydraulic motor unit includes a hydraulic motor main body, a motor shaft, a motor case and a port block. The port block includes a motor surface to which the motor case is connected, a pump surface to which a pump case surrounding a hydraulic pump main body is detachably connected so as to form a pump space for accommodating the hydraulic pump main body, and a pair of operational fluid passages fluidly connecting between the hydraulic motor main body accommodated in the motor space in a state of being contacted with the motor surface in a sliding manner around its axis line and the hydraulic pump main body accommodated in the pump space in a state of being contacted with the pump surface in a sliding manner around its axis line.