PURPOSE: To make a close range examination possible of an examinee whose eyes are rather close each other and to easily adjust refraction angles of the prism devices for convergence of gaze, by making the refraction angle of at least one of the two prism devices 1 or 2 changeable using an electric driving device.

CONSTITUTION: The device has the 1st prism device 25 composed of more than one prisms 23 with different fraction angles which are arranged with a certain interval on the periphery of the disk 24 to the direction of the periphery, and the rotary prism 26 as the 2nd prism device. This rotary prism 26 consists of a pair of ring-shaped prism plates 27 and 28. By relatively rotating these ring-shaped prism plates, the refraction angle can be changed optionally. In this case, the disk 24 of the 1st prism device 25 and the ring-shaped prism plates 27 and 28 of the rotary prism 26 are driven to rotate by the pulse motor (electric driving device). The mechanism on the right side is the same. Accordingly, the close range examination is possible without widening the lens housing.