PURPOSE: To accurately detect a fret operation position and easily use printed resistances even when resistors are all equal in resistance value by supplying the constant current from a constant current source to the respective resistors which are connected in series between electrodes of fret switches.

CONSTITUTION: The fret switches FSW which have movable electrodes and fixed electrodes respectively are provided between the frets 28 provided on the top surface of the neck 22 of the electronic stringed instrument such as a guitar, resistance circuits 110 having the same resistance values are provided between those electrodes, and a constant voltage source is connected; and a pickup group 42 is used corresponding to the vibrations of strings and fret operation positions are detected by the strings. Namely, the vibrations of the strings 24-1 to 24-6 are detected by pickups 28-1 to 28-6 and electric signals corresponding to them are supplied to an amplitude value detecting circuit 43; and a CPU 41 is interrupted for peak value detection and when the peak value is larger than the specific value at the on start, pitch information is stored in a RAM 48, thereby varying and controlling the loudness of a sound source 44 corresponding to envelope signals from the strings.