A beam irradiation device includes: a laser light source for emitting laser light; an actuator which scans a targeted area with the laser light; a servo optical system which changes a propagating direction of servo light in response to driving of the actuator; a photodetector which receives the servo light to output a signal depending on a light receiving position of the servo light; an actuator controlling section which controls the actuator based on the signal to be outputted from the photodetector; and a laser controlling section which controls the laser light source based on the signal to be outputted from the photodetector. The laser controlling section controls the laser light source to emit the laser light in a pulse manner at a timing when the light receiving position of the servo light coincides with a predetermined targeted position.