To provide a substance detector for detecting the presence of a plurality of substances to be detected in a solution, using a substance detection plate of a very simple structure, without having to require calibration of signal, and to quantitatively evaluate the substances to be detected.

The substance detector includes: the substance detection plate obtained by forming a substance responsive film on a semiconductor; a means for bringing the solution containing the substance to be detected into contact with the surface of the substance responsive film; a means for stabilizing the potential of the solution; a means for irradiating the substance detection plate with a pulse laser beam, to generate a pulse electromagnetic wave having amplitude intensity, depending on the amount of the substance to be detected at the irradiation position; a means for measuring the amplitude intensity of the pulse electromagnetic wave; and a means for determining the presence of the substance to be detected from the amplitude intensity.