Before detecting the surface state of specific patterns a sample by means of an electron beam tester system, patterns formed in a specified surface area of the sample, are detected by deflecting an electron beam by a deflection coil. Data representing current supplied to the deflection coil, data representing the position of the sample during the pattern-detecting operation, and image signals representing the patterns found in the specified surface area, are stored in a memory. While the specific patterns of a sample are being detected, the electron beam is used to perform a second pattern-detecting operation. Data representing current supplied to the deflection coil during the second pattern-detecting operation, such data representing the position of the sample, and image signals provided by the second pattern-detecting operation representing the patterns formed in the specified surface area, afe compared with those data items already stored in the memory. From the difference between the compared two sets of data items, any drift in the electron beam is calculated. In accordance with the drift thus calculated, the deflection coil is energized to deflec the electron beam such that the beam is applied onto the desired portion of the sample.