To provide a handwriting input system capable of dispensing with an operation of a button or the like in both on-line and off-line, easy to write by handwriting, and capable of supporting an input by a gesture.

This handwriting input system includes an information processor for converting position coordinates of an electronic pen into a holograph data, the electronic pen automatically transmits an ultrasonic signal and an infrared signal as a gesture data of a motion locus of the electronic pen, at a non-writing time after transmitting the ultrasonic signal and the infrared signal used for detecting a holograph, and the information processor receives the holograph data and the gesture data transmitted from a receiver, converts the received holograph data into a display data for display, compares the gesture data with a locus of a gesture stored preliminarily in the information processor, and executes a corresponding command, when the gesture data transmitted from the receiver is matched with the locus of the gesture stored preliminarily in the information processor.