TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: For the target, when all hydrogen atoms are exhausted by removing and oxidizing. Hydroxyl group is continuously oxidized by taking hydrogen atom from water molecule. While these are recycled into water and extracted out of the system, hydrogen of nascent state is produced generating an oxygen molecule. Hydrogen of nascent state reduces and hydrogenates the target from which all hydrogen atoms are taken. While a carboxyl group is included by the hydroxyl group, a valence electron moves with double-bond formation of the oxygen atom. Carbon dioxide gas is produced and extracted out of the system. In the case of aldehyde group having hydrogen atom, by addition and hydroxyl-group-formation of hydroxyl group continuously to the vacancy of hydrogen atom taken, a valence electron moves with double-bond formation of the oxygen atom continuously. Carbon dioxide gas is produced and extracted out of the system. In the case of methylene group having hydrogen atom, addition and hydroxyl-group formation is carried out continuously to the vacancy of hydrogen atom taken. A valence electron moves with double-bond formation of the oxygen atom. Carbon dioxide gas is produced and extracted out of the system. In the case of methyl group having hydrogen atom, addition and hydroxyl-group-formation is carried out continuously to the vacancy of hydrogen atom taken. A valence electron moves with double-bond-formation of the oxygen atom continuously. Carbon dioxide gas and an oxygen molecule are produced and extracted out of the system. In the case of carbonyl group, a valence electron moves with addition and hydroxyl-group-formation and double-bond formation of oxygen atom are carried out continuously. Carbon dioxide gas is produced and extracted out of the system. In the case of ether group, with addition of hydroxyl group, hydroxyl-group-formation, and double-bond-formation of oxygen atom, a valence electron moves, and an oxygen molecule is produced and extracted out of the system. The required total number-of-moles of hydroxyl group which an oxidative decomposition of the target requires is computed based on reaction formula. Hydroxyl group is produced by Fenton method, and the additional amount of hydrogen peroxide and a bivalent iron ion is computed based on the required total number-of-moles of hydroxyl group. While the concentration of the component is detected by a detector (12), the structural component and the number-of-moles of the component are input by an input unit, based on the concentration detected of the target and the input structural component, and the number-of-moles. By a control apparatus (11), the required total number-of-moles of hydroxyl group which an oxidative decomposition of the target requires, and the additional amount of hydrogen peroxide and a bivalent iron ion are computed. Based on the indications from the control apparatus, hydrogen peroxide of the additional amount and a bivalent iron ion are added by a hydrogen-peroxide-addition unit (9) and iron-ion addition unit (10) with respect to the aqueous solution. The control apparatus consists of a computer (14). Arithmetic processing of the required total number-of-moles of hydroxyl group, and the additional amount of hydrogen peroxide and bivalent iron ion is carried out. The data stored beforehand is searched and the number-of-moles of hydroxyl group required is extracted by a program.