PURPOSE: To increase measuring angles by combining a plate cam, levers and parallel flat plate glass so as to offset errors produced by the same thereby reducing the errors contained in read values and increasing the oscillating angle of the parallel flat plate glass.

CONSTITUTION: Glass 4 is inserted in the luminous flux 6 from a horizontal scale disc in such a way that the luminous flux from the horizontal scale disc is reflected by a prism 11 and is then made incident to a prism 12, from which the flux is conducted to a telescope part. The parallel flat plate glass 4 is fixed to the 2nd lever 8 by determining its direction in such a way that when the 1st, the 2nd levers 3', 8' are in the intermediate position in the respective oscillating ranges the flux 6 from the horizontal scale disc is made incident perpendicularly to said glass. When a rotary handle 1 is turned, a plate cam 2 and a scale disc 5 for reading of micro-angles rotate together, and as the cam 2 rotates, the lever 3' oscillates. Then the lever 8 in abutment on the cam follower 30' of the 1st lever oscillates and at the same time the glass 4 oscillates.