NOVELTY - The method involves injecting one type of gas remainder in reaction container from injection opening among multiple types of gases. The injection opening (2a) is arranged inside of tubular portion which is installed in reaction container (1). One type of gas is injected toward one end side of tubular portion from injection opening. The gas in reaction container is flowed into inside of tubular portion from opening portion of other end side of tubular portion, and is flowed out of one end side of opening portion.    USE - Gas reaction method for producing hydrogen selenide used as raw material of copper indium gallium selenide (CIGS) type solar cell.    ADVANTAGE - The gas does not use for hydrogen selenide in large quantities, and the production amount of per unit time of target compound is high.    DETAILED DESCRIPTION - The method involves arranging injection opening to the axial direction inside of tubular portion rather than the opening portion of one end side of tubular portion. The source material is arranged on the inside of reaction container, and is vaporized within the reaction container. One type of gas is injected toward the source material from the injection opening, while arranging the source material on the bottom portion inside the reaction container and vaporizing within the reaction container. One type of gas is selenium, and the remainder gas is hydrogen gas. An INDEPENDENT CLAIM is included for a reaction apparatus has a gas supply portion that is equipped with the raw material accommodating portion which accommodates the source material of liquid used as generation source of one type of gas, or solid state. A heating portion is provided to heat the raw material accommodating portion (6), and to vaporize the source material. The raw material accommodating portion is provided in the inside of reaction container.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view illustrating the gas reaction process.    Reaction container (1)    Inner tube (2)    Injection opening (2a)    Heater (5)    Raw material accommodating portion (6)