To achieve endoscopic surveillance with an optical fiber in an image with a high depth of field by newly designing a microlens using an aspherical single lens.

The optical fiber is fixed in a back-focus position of the aspherical single lens having an outer diameter of about 0.5 mm. Thus, in a single lens, an observation with a high depth of field can be achieved within a total view angle of 70 to 80° and in a working distance from about 2.5 mm to infinity.