A mower unit (120) comprising a blade unit (170) including: a rotary shaft (171a, 173a) having a rotary axis (171, 173) extending in a vertical direction; and a blade (172, 174) which is provided on the rotary shaft (171a, 173a) and rotatable about the rotary axis (171, 173); a blade housing (121) including a top panel (121a) and a side plate (121b) extending downward from a peripheral edge of the top panel (121a), for covering the blade unit (170) from above to create a mowing space (108) therein; a mown grass discharge port (129) formed in the top panel (121a) for discharging conveying air flow generated by rotation of the blade; an intake part (102) that supplies ambient air to the conveying air, the intake part (102) includes an ambient air intake opening (102a; 102b; 102c) formed in mown grass discharge port (129) or in the vicinity thereof, and an auxiliary ambient air intake opening (121s; 121e; 121f; 121g) formed in the top panel (121a) or the side plate (121b); and a cover (200; 201; 202; 203; 125a)
