A metal film of a measurement device including a transparent dielectric substrate is irradiated with first light from a transparent dielectric substrate side, an optical electric field enhanced by an optical electric field enhancing effect of a localized plasmon induced to a surface of the metal film by the irradiation is generated, light emitted from the transparent dielectric substrate side is detected, a specimen installed on a surface of a metal fine concavo-convex structure layer and a matrix agent are irradiated with second light from a side opposite to the side of the irradiation with the first light in a state where a voltage is applied to the metal fine concavo-convex structure layer through a voltage application electrode, an analysis target substance for mass spectrometry in the specimen is desorbed from the surface by the irradiation, and the desorbed analysis target substance is detected.