To provide a compass which has an ultrasmall shape and enables circular or arc-shaped line drawing or cutting to be performed with accuracy.

This compass is attached to a ruler so that the ruler can be used as the compass, and high dimensional accuracy is realized by using a scale on the ruler. The compass is composed of a writing instrument or a cutter fixing component A, a rotating shaft component B and the ruler C. Temporary fixing knobs are attached to the components A and B. The ruler C has a scale and is linearly formed. A forward end of the ruler C is inserted into a ruler inserting port 3 of the component A, and fixed by the temporary fixing knob 1. The component B can be slid in the longitudinal direction of the ruler C after the ruler C is inserted into a ruler inserting slit 4.