The apparatus for ion beam fabrication, which has been able to detect any anomalous condition of ion beams only by means of the current irradiated on the specimen, could not compensate the failure by investigating the cause and could not realize stable processing. To solve the problem described above, the present invention includes the first and second blankers and Faraday cups switches ON and OFF the first and second blankers and monitors beam current at two positions above and below the projection mask. By adopting this configuration, it will be possible to acquire the information on failure in ion beam, sort out the cause of the failure and to compensate the failure while limiting damages to the projection mask. As a result, it will be possible to realize stable processing by means of ion beam, and to use the ion beam fabricating device on a stable basis.