An electronic musical instrument provides an automatic tonality designating function capable of automatically designating a desirable tonality based on a chord and a rhythm kind which are respectively designated. The chord is designated by simultaneously depressing plural keyboard keys, while desirable one of plural rhythm kinds which are predetermined in advance is designated by the performer. In addition, a desirable mode can be determined based on the designated chord. Based on the mode, chord and rhythm kind, an automatic accompaniment can be performed. Further, this electronic musical instrument can also provide a chord detecting apparatus capable of automatically detecting a desirable chord based on plural notes (or note names) designated by the performer. In such chord detection, an evasive note is automatically omitted from all notes designated by the performer, so that the desirable chord can be detected with accuracy.