A treatment apparatus for analyzing the impurities in silicic material with high precision, includes a container having an inner space in which at least one analysis sample container and a sample decomposing solution are accommodated. The container is divided into a lid body and a lower body, each of the lid body and the lower body being opened at the division surface side thereof to form an open end and being closed at the surface side opposite to the division surface side to form a close end thereof. The inner peripheral surface of the open end of the lower body is formed in a stepwise shape so that the analysis sample container is disposed to be spaced from the surface of the decomposing solution which is stocked in the lower body, and the inner peripheral surfaces of the lid body and the lower body are smoothly continuously threadily engaged with each other through abutment faces thereof to keep the container in an appropriate hermetic level. Through the analysis process using the apparatus, the impurities contained in silicic materials used for semiconductor industries in which integration techniques are remarkably developed can be quantitatively analyzed in the order of ppt to obtain silicic products having high reliability.