PURPOSE: To subject the surface of a solid sample to a surface treatment to a uniform state by using a gas supplying pipe made into double construction consisting of an inside pipe and outside pipe to supply various gases at the time of bringing various gaseous raw materials into reaction with light to decompose the same and treating the surface of the solid sample.

CONSTITUTION: A material 3 to be treated is placed in a reaction chamber 8 and the various reactive gases are supplied from the gas supplying pipe 1. Light is irradiated from upper light sources 4 to the gases to induce the decomposing reaction therein. The surface of said material is treated by the generated active chemical seed, the resulted product of the photodecomposition and the light arriving at said material. The gas supplying pipe 1 is made into the pipe of the double construction consisting of the inside pipe 21 and the outside pipe 22 in this case. The various gases raw materials are supplied from a gas introducing pipe 20 into the inside pipe 21 and are ejected into the spacing between the inside pipe 21 and the outside pipe 22 from ejection ports 23 provided on one side. The ejected gases are stagnated, filled and equalized in pressure in the space between the inside pipe 21 and the outside pipe 22 and are supplied from ejection ports 24 provided on the surface of the outside pipe on the side opposite by 180° from the ports 23 into the reaction chamber 8. The surface of the material 3 is thus treated always in a uniform state.