A running mower of the present invention comprises a traveling body 1 provided, between the front wheels 2 and the rear wheels 3, with a rotary mowing unit 12 which includes a laterally spaced pair of mowing blades 16a, 16b. The traveling body is also provided with an outlet duct 26 extending backward from between the mowing blades past a position between the rear wheels for discharging grass mown by the mowing blades. The rotary mowing unit 12 is provided with a forwardly extending mower input shaft 22 disposed offset from the center of the mowing blades toward one mowing blade 16b by an appropriate amount L1. A front part of the traveling body 1 is provided with an engine 4 whose power is transmitted to the input shaft via a mower transmission shaft 23 having a respective end provided with a universal joint 23a, 23b. As a result, the power transmission from the engine to the rotary mowing unit is simplified while the mown grass is disposed smoothly from the outlet duct 26.