In order to implement a high-sensitivity mass spectrometry through an improvement in solvent removal efficiency during electrospray ionization and the like, an ionization device is provided with a light guide path 28 which guides light from a light source to sample microparticles generated by a micronization device to irradiate the microparticles. A closest distance d2 between a spatial area 34 in which the sample microparticles are present and a distal end 29 of the light guide path is greater than or equal to 0.1 mm and less than or equal to 20 mm. A closest distance d1 between an area of light irradiation 35 by the light guide path and any of a sample surface, a micronization device, and a sample holding unit that is the closest is greater than or equal to 0.01 mm and less than or equal to 10 mm.