A grass mower comprising: an engine; a mower unit that is coupled to a vehicle body frame via parallel links so as to be raiseable and lowerable; a grass collection duct configured to guide cut grass from the mower unit toward the rear of the vehicle body; and a grass collection container configured to store the cut grass guided by the grass collection duct, wherein the grass collection duct includes: a first bottom plate attached to the mower unit side; a second bottom plate attached to the vehicle body frame side so as to be able to swing up and down; a first duct upper body that is attached to the mower unit, and a second duct upper body that is attached to the vehicle body frame and whose front end portion is formed widely so as to cover the rear end portion of the first duct upper body from above; and a connection mechanism configured to swing the second bottom plate up and down in conjunction with raising and lowering of the mower unit, and the grass mower is further configured so that in a state in which the mower unit is in contact with the ground, the connection mechanism connects the mower unit and the second bottom plate such that the front end portion of the second bottom plate is near to the rear end portion of the first bottom plate, and as the mower unit rises rearward and upward, the second bottom plate swings in a forward-rising direction and the rear end portion of the first bottom plate goes below the second bottom plate while the state of being near to the second bottom plate is maintained; and characterized in that a front end portion of the second bottom plate is formed in a tapered shape that falls within the left-right width of the first duct upper body. an engine; a mower unit that is coupled to a vehicle body frame via parallel links so as to be raiseable and lowerable; a grass collection duct configured to guide cut grass from the mower unit toward the rear of the vehicle body; and a grass collection container configured to store the cut grass guided by the grass collection duct, wherein the grass collection duct includes: a first bottom plate attached to the mower unit side; a second bottom plate attached to the vehicle body frame side so as to be able to swing up and down; a first duct upper body that is attached to the mower unit, and a second duct upper body that is attached to the vehicle body frame and whose front end portion is formed widely so as to cover the rear end portion of the first duct upper body from above; and a connection mechanism configured to swing the second bottom plate up and down in conjunction with raising and lowering of the mower unit, and the grass mower is further configured so that in a state in which the mower unit is in contact with the ground, the connection mechanism connects the mower unit and the second bottom plate such that the front end portion of the second bottom plate is near to the rear end portion of the first bottom plate, and as the mower unit rises rearward and upward, the second bottom plate swings in a forward-rising direction and the rear end portion of the first bottom plate goes below the second bottom plate while the state of being near to the second bottom plate is maintained; and