To securely support and protect a belt pulley type infinite variable- speed drive on an agricultural working car.

A driving pulley 21 and a driven pulley 23 around which a belt 24 is wound, their fixed sieves 25, 39, an arm part 34b as a working mechanism of movable sieves 26, 41, a driving rod 37 a head end of which is connected to it, an arm part 45b and a driven rod 48 a head end of which is connected to it are arranged in a space surrounded by a front and rear longitudinal main frame 80 of a car body frame 2, an engine 5 and a transmission case 6 in a plan view. A cover part 29b of a support body 29 used, indual purpose, for a cover fixing a base part 29a on a side surface of the engine 5 with a bolt 110 is made cover the front surface of an outer periphery of the driving pulley 21, a fixed sieve 25 is fixed on an inner surface of a head end supporting part 29c extending backward from the cover part 29b and a hydraulic pump 104 is fixed on an outer surface. A rear end of the head end supporting part 29c is fixed on the main frame 80 through a connecting bracket 106.