To increase the biting speed to a screw, the reaction speed of an unnecessary plant with enzyme and the return speed to soil in a plant crusher.

In a state held to a predetermined temperature range by a heater for heating a crushed plant C housed in a housing container 2, heavy lumps A and B large in mass are upwardly fed by the rotation of a screw 8 while stirring the crushed plant C housed in the housing container and repeatedly dropped on the crushed plant C to convert the crushed plant C to a liquid powder. The plant C bonded to the inner surface of the housing container 2 is scraped off by the rotary stay S1 rotated along with the screw 8 by attaching the rotary stay S1 to the spiral plate 10 of the screw 8 in the vicinity of the upper end thereof and a plant low in specific gravity such as a weed or the like can be smoothly bitten by the screw 8.