A grass mower includes a raiseable and lowerable mower unit (7) and a grass collection duct (8) that guides cut grass rearward from the mower unit (7). The grass collection duct (8) includes: a first bottom plate (31) on the mower unit side, a second bottom plate (41) on the vehicle body frame side that can swing up and down, and a connection mechanism (43) that causes the second bottom plate (41) to swing up and down in conjunction with raising and lowering of the lower unit (7). In a state in which the mower unit (7) is in contact with the ground, the connection mechanism (43) connects the mower unit (7) and the second bottom plate (41) such that the front end portion of the second bottom plate (41) is near to the rear end portion of the first bottom plate (31) and as the mower unit (7) rises rearward and upward, the second bottom plate (41) swings in the forward-rising direction and the front end portion of the first bottom plate (31) goes below the second bottom plate (41) while the state of being near to the second bottom plate (41) is maintained.