melody and chord information of a music piece are supplied . on the basis of the chord information , one or more possible musical keys are nominated . then , on the basis of the melody information , it is judged in a collating manner whether it is proper to determine any of the possible musical keys as a musical key of the music piece . for instance , the possible musical keys are nominated on the basis of detection of a dominant motion , since the dominant motion in a chord progression strongly suggests specific musical keys . for instance , of the nominated possible musical keys , those which do not contain all of the melody notes as their scale note are excluded , and a single musical key which contains all of the melody notes as its scale note is determined as the musical key of the music piece . with such arrangements , it is allowed to make a musical key determination which is very reasonable from a musical point of view .