PURPOSE: To make the device inexpensive and compact, by providing counting means which electrically count the rotary angle in a telescope fine adjusting mechanism, and making it possible to read the interpolation within the lowest readable unit.

CONSTITUTION: A tightening handle 110 is untightened, and an angle point to be measured Pm is collimated with a center 200a of a cross lines 200. A this time, a reading means and pulse generator 153-1 outputs a main measuring angle scale output pulses corresponding to the rotary angle of the telescope to a counter 158-1. The counted value is inputted in an adder 159. Then the tightening handle 110 is tightened so as to engage a tightening frame 106 with a rotary shaft 101. Then a fine adjusting knob 117 is rotated so as to rotate the tightening frame 106 until the Pm is aligned with the center 200a. At this time, the main scale output pulses are outputted from the circuit 153-1 to the counter 158-1 by the rotation of the rotary shaft 101. At the same time, the vernier scale pulses are outputted from a pulse generating circuit 153-2 to a counter 158-2. The rotary angle is displayed 7 through the adder 159 and an operator 161.