PURPOSE: To improve working efficiency and safety by evaporating and splashing the acid penetrated in a porous susceptor and decomposing and removing the deposits of the wall of a reaction tube.

CONSTITUTION: The susceptor 4 consisting of a porous material is immersed into an acid soln. 8 in a beaker 7 to penetrate the acid into the porous material. After this susceptor 4 is dried to the extent that the surface dries and the acid remains in the inside, the susceptor 4 is installed in the reaction tube 1 of the MO-CVD device and the acid in the susceptor 4 is evaporated by the high-frequency heating by an RF coil 3, by which the acid is splashed in the reaction tube 1. The deposits 2 of the tube wall and the acid react with each other, by which the deposits are decomposed and removed. The need for removing the reaction tube 1 is eliminate by this method. The working efficiency is improved and the high safety id obtd. even when the deposits contain arsenic.