The electron beam irradiating apparatus with the monitoring device has an electron beam irradiating means for irradiating materials in an irradiation chamber. The monitoring device has a photographing means for imaging a lights emitted by irradiating an electron beam to the materials; a storage means that stores state of electron beam irradiation in advance; and a calculating means that processes an image, which is captured by the photographing means, to decide a state of electron beam irradiation. The storage means has stored at least three state of electron beam irradiation and also has stored image luminance associated with those states of electron beam irradiation. The calculating means loads the image, which is captured by the photographing means, to compare the loaded image with the image luminance stored in the storage means, thereby deciding a state of electron beam irradiation.