A device for adjusting the tension of the strings of a guitar having at least two strings, particularly an electric guitar or a bass, particularly an electric bass, in which each string of the guitar or bass is, with one end, wound on a turning peg of an adjusting mechanism mounted on the neck of the guitar or of the bass. The adjusting mechanism contains a combination consisting of a worm shaft and of a worm wheel and, due to these, is provided with a self-locking ability. The aim of the invention is to improve the design of a device of the aforementioned type so that, without considerably altering the basic shape of the guitar or of the bass, this device can automatically adjust the tension of individual strings of the instrument reliably and precisely whereby ultimately enabling them to be tuned. To this end, a drive unit for each adjusting mechanism is mounted on the neck of the guitar or of the bass. The drive unit is directly connected to the worm shaft or to the worm wheel (17) of this adjusting mechanism in order to drive the worm shaft or the worm wheel.