A pen input apparatus of the present invention is provided with an apparatus for detecting an inclination of an input pen. The apparatus for detecting an inclination of an input pen is composed of a hemispherical container, a conductive movable body, and detecting means. The hemispherical container, in which a hemispherical cavity is created, has an axis congruent with the axis of the input pen, and is provided so as to integrally move with the input pen, while a plurality of ring-shaped electrodes are concentrically provided with the input pen. The conductive movable body is provided in the hemispherical cavity, and moves according to the inclination of the input pen due to gravity. The detecting means detects the position of the movable body in the hemispherical cavity in accordance with how continuity is between the ring-shaped electrodes, and detects an inclination of the input pen in accordance with the detected position of the movable body. The pen input apparatus has a simple structure, and is superior in the response speed, since the inclination of the input pen is detected without detecting coordinates.