PURPOSE: To measure a deflecting response of an electron beam in an electron beam work machine in accordance with an actual condition of use, by measuring the relation between an irradiated position of the electron beam according to the lapse of time and an elapsed time.

CONSTITUTION: A current value changed in a stepping state is applied to deflecting coils 6, 7 for deflecting an electron beam 8 to measure a difference, between a target electron beam position after a transient response end of current in said deflecting coils generated from said change and an electron beam position for each time before said transient response end, at said each time, and a required time till the electron beam reaches a predetermined permissible range from said target electron beam position is decided from the above measurement result. Accordingly, if a permissible amount of position shifting corresponding to each deflecting distance is given, after a change of the deflecting coil current is applied, how long an elapsed time is taken to enable correct beam irradiation can be predetermined, and correct beam work control can be realized.