Proposed is a device for detecting a chemical/physical phenomenon, in which, via a novel scheme, charges are accumulated in a charge accumulation region. An amount of charges thus accumulated reflects the potential of a sensing region and the potential corresponds to an external environment (chemical phenomenon or physical phenomenon) to be detected. A charge accumulation region 5 includes a first potential well region FD1 that is continuous with a sensing region 3, the boundary potential of the charges held in the first potential well region FD1 being made equal to the potential of the sensing region 3, whereby the potential of the sensing region 3 is made to be reflected in the amount of charges held in the first potential well region FD1.