An electron beam radiation device having an electron beam detecting device configured to detect a state of an electron beam radiated by the electron beam radiation device, wherein: the electron beam radiation device has a plurality of filaments for emitting thermal electrons each of the filaments radiates electron beams forming a plane containing the filament, and the electron beam detecting device comprises: a plurality of conductors corresponding in number to the plurality of filaments and disposed corresponding to the plurality of filaments such that each conductor is arranged on a line in the plane formed by the radiated electron beams of a respective one of the plurality of filaments, the conductors being electrically insulated from each other, in the area in which the electron beams are radiated; a measuring unit for measuring the current value flowing through each of the conductors; and a determining unit for determining the radiation level of the electron beams by receiving a signal output by the measuring unit, the determining unit being arranged to judge that, when the measuring unit measures a decrease in the electrical current value, an abnormal condition exists in the filament corresponding to the conductor in which the lower current value is detected. the electron beam radiation device has a plurality of filaments for emitting thermal electrons each of the filaments radiates electron beams forming a plane containing the filament, and the electron beam detecting device comprises: a plurality of conductors corresponding in number to the plurality of filaments and disposed corresponding to the plurality of filaments such that each conductor is arranged on a line in the plane formed by the radiated electron beams of a respective one of the plurality of filaments, the conductors being electrically insulated from each other, in the area in which the electron beams are radiated; a measuring unit for measuring the current value flowing through each of the conductors; and a determining unit for determining the radiation level of the electron beams by receiving a signal output by the measuring unit, the determining unit being arranged to judge that, when the measuring unit measures a decrease in the electrical current value, an abnormal condition exists in the filament corresponding to the conductor in which the lower current value is detected. a plurality of conductors corresponding in number to the plurality of filaments and disposed corresponding to the plurality of filaments such that each conductor is arranged on a line in the plane formed by the radiated electron beams of a respective one of the plurality of filaments, the conductors being electrically insulated from each other, in the area in which the electron beams are radiated; a measuring unit for measuring the current value flowing through each of the conductors; and a determining unit for determining the radiation level of the electron beams by receiving a signal output by the measuring unit, the determining unit being arranged to judge that, when the measuring unit measures a decrease in the electrical current value, an abnormal condition exists in the filament corresponding to the conductor in which the lower current value is detected.