The present invention provides a reaction device for producing trichlorosilane and a preparing method thereof. The reaction device reliably disperses the hydrogen chloride gas, further increases the production efficiency of trichlorosilane and reduces the generation of silicon tetrachloride to the utmost. The reaction device (10) which is used for producing trichlorosilane and leads to the reaction of the metallic silicon powder (M) and the hydrogen chloride gas is provided with a device body (11) that is supplied with metallic silicon powder (M), and a jetting outlet which jets the hydrogen chloride gas from the base of the device body (11) into the device body (11) sideways. The upside of the jetting outlet is stacked with a plurality of small sheets with through holes passing through along the thickness direction, and a plurality of particles which are clamped between the small sheets with through holes.