Abstract: A thread tension adjusting apparatus, used in a sewing machine, adjusts tension of a supplied thread by adjusting a thread holding force. The apparatus is provided on a thread supply path running from a thread source to a thread processing section such as a needle and a looper. The thread tension adjusting apparatus comprises a pair of members respectively having portions opposed to each other. At least one of the members is a piezoelectric actuator for changing a distance between the portions when being driven, whereby to adjust a thread holding force.