An ionization device including: a laser light source; a light collection optical system configured to irradiate a sample with the laser light; a first intensity changing unit configured to continuously change an intensity of laser light; a second intensity changing unit configured to stepwisely change an intensity of laser light; an irradiation diameter setting reception unit configured to receive setting of an irradiation diameter of laser light; an irradiation intensity setting reception unit configured to receive setting of an irradiation intensity of laser light; and a laser light intensity controller configured to set an intensity of the laser light by changing an irradiation diameter of the laser light by the light collection optical system and controlling the second intensity changing unit according to the irradiation diameter, and by controlling the first intensity changing unit according to the irradiation intensity.