To avoid unstable light radiation during switching of a phase modulation amount and stimulate desired stimulation points simultaneously, provided is a photo-stimulator which includes an AOM switching on/off of radiation of stimulation light to a specimen S; an LCOS-SLM being capable of modulating a phase of stimulation light once radiation to the specimen S has been turned on by the AOM; and a controller controlling the LCOS-SLM to switch a phase modulation amount of stimulation light and controlling the AOM to switch on/off of radiation of stimulation light, wherein the controller causes the AOM to turn off radiation of stimulation light before the LCOS-SLM starts switching a phase modulation amount, and causes the AOM to turn on radiation of stimulation light after the LCOS-SLM completes switching a phase modulation amount.