Provided is a riding type mowing machine in which an upper surface of a mower deck (8) is provided with a transmission mechanism (9) and an upper surface of the transmission mechanism (9) is covered by a cover body (K) detachably attached to the mower deck (8), the cover body (K) includes a left cover body (12) covering a left end portion of the transmission mechanism (9), a right cover body (13) covering a right end portion of the transmission mechanism (9), and a center cover body (14, 15) covering a center portion of the transmission mechanism (9), and the rigidity of the left cover body (12) and the right cover body (13) is set to be higher than the rigidity of the center cover body (14, 15).