To provide an electron beam irradiation device capable of reducing quantity of inert gas consumed while maintaining oxygen concentration in an irradiation chamber in appropriate level. An electron beam irradiation device to irradiate an electron beam to an irradiated object passing through an irradiation chamber while introducing inert gas into the irradiation chamber comprising an oxygen concentration detection device to detect oxygen concentration in the irradiation chamber; a main controlling valve to regulate flow rate of inert gas introduced in the irradiation chamber; a control unit to control valve travel of the main controlling valve so that the flow rate of the inert gas decreases when the oxygen concentration becomes low on the basis of the oxygen concentration detected by the oxygen concentration detection device.