PURPOSE: To observe wide range of direction of thickness of a specimen at high resolution by providing a device that splits optical path into more than two behind an objective lens and making image pickup faces provided in each optical path conjugate at different positions in front of the objective lens.

CONSTITUTION: A device 2 that splits an optical path into three is provided behind the objective lens 1, and an image pickup face S' is provided in each split optical path (l). Positions S1WS3 in the direction of thickness of a wafer, a specimen on the stage, are observed at image pickup faces S1'WS3' which are at conjugate position. The observation can be made on desired one layer or on the face of many layers. Accordingly, the simutaneous observation of wide range can be made superposing different faces in the direction of thickness of the specimen in spite of its high resolution.