A three‐circle goniometer for a large‐hole electron‐paramagnetic‐resonance (EPR) cavity is described which, by a very simple operation, enables us to rotate the crystal around arbitrary direction parallel to the static magnetic field, by rotating a sample holder about a redundant (or the third) axis accommodated in a spur and crown gear. By comparing not only the observed resonance field with the calculated one, but also the absorption intensity with the transition probability, the quantitative determination of the concentration of the unpaired electron center in a single crystal is possible.