Abstract: A pen-type computer input device is used to move a cursor on the display of a computer system or enter data such as of figures, letters, numerals, or the like into a computer system. The pen-type computer input device includes a shank, a ball rotatably supported on the tip end of the shank, a pair of rotatable members rotatable about X and Y axes extending perpendicularly to each other and held in rolling contact with the ball, and a rotation detector for detecting the direction in which the rotatable members rotate and the distance by which the rotatable members move. Since the rotation of the ball is directly transmitted to the rotatable members and the distance by which the rotatable members move is detected, the pen-type computer input device is small in size and can easily be handled.