PURPOSE: To avoid data sampling mistake, by displaying the code of the input signal for every pen when the pen makes recording.

CONSTITUTION: The display elements 3 and 5 such as numeric display elements are fitted to the pen heads 2a and 4a, and they are connected to the decoder driver 8 via the pen head display sections 6 and 7. Thus, the decoder driver 8 receives the input signal from the input signal selection section 9 and the signal representing the combination of the pens 2 and 4 recording the signal to record the input signal designated to the designated pens 2 and 4. The signal designating the number representing the input signal designated is fed to the pen head display sections 6 and 7 of the pens 2 and 4 to display the designated number of the display elements 3 and 5. Thus, the mistake in the data sampling due to wrong input signal selection can be avoided.