A decomposition apparatus and a decomposition method using the apparatus in which a substance to be decomposed is decomposed with high efficiency are disclosed. A decomposition apparatus includes condensation means for increasing the concentration of the substance, and decomposition means provided with a decomposition chamber (predetermined space) for receiving and decomposing the substance. The substance of which concentration is increased by the condensation means, in a gaseous state, is directly transported to the decomposition chamber and is decomposed.