PURPOSE: To observe a microbe or the like with a proper magnification adapted to its size and observe it precisely with a high magnification by moving an intermediate lens constituting an expanding means to change the length to an objective lens.

CONSTITUTION: When a motor 7 dries a plunger 2 to the cover glass side to fix a liquid passing part 1 between the plunger 2 and a transparent glass 8 and an illuminating light is led by an optical fiber 6, the image of a water to be examined to which the light condensed by a lens 5 is projected is expanded by an expanding means 12 consisting of an objective lens 9, an eyepiece lens 11, and an intermediate lens 22 and is picked up by a television camera 13 When focusing is necessary, the lens 9 is moved by a motor 27 and the lens 22 is moved by a motor 23. The expansion rate is changed by these movements. In case of observation in a wide range, the television camera 13 and the expanding means 12 are moved in X-axis and Y-axis directions by motors 15 and 18. Thus, all of the surface in the fixed part of a water to be examined of the plunger 2 is observed.