Abstract: A cursor control device construction includes a body accommodating a circuit board and having a circular hole in a bottom side for containing a ball which may move freely therein. The body further has a pair of encoders, each of which consists of a wheel, a light source and a sensor. The wheel, light source and sensor may be secured on a securing seat which are provided with insert means at a bottom side thereof for insertion into corresponding holes in the circuit board. The securing seat further supports an idle wheel which is disposed between a roller at an end of a spindle of the wheel and the ball for transmitting rolling actions of the ball to the roller, so that when the ball rotates, the wheel is caused to synchronously rotate therewith.