To provide a supercritical water reaction device facilitated in the maintenance and having high profitability.

The supercritical water reaction device 10 is a device for treating water slurry of a pulverized organic solid with the supercritical water reaction and has the same structure of a reactor and the flow-out line of a reaction product as that of the conventional supercritical water reaction device. The supercritical water reaction device 10 is provided with 2 extrusion piston pumps 12A, B provided in parallel arrangement, a tank 13 for the liquid to be treated, which is for housing the liquid to be treated, and a pump for the liquid to be treated, which is for feeding the liquid to be treated to the extrusion piston pump from the tank for the liquid to be treated. A water tank 15 for housing the water and a water forcibly feeding pump 16 for forcibly feeding the water to the extrusion piston pump from the water tank 15 are provided as a driving means for the extrusion piston pump and further a hydrogen peroxide tank 17 for housing hydrogen peroxide as an oxidizing agent and a hydrogen peroxide pump 18 for feeding the hydrogen peroxide to the reactor are provided.