A processing apparatus comprising: a main body side equipped with a power supply unit that outputs AC voltage; a tool side rotatable in relation to the main body side and equipped with an ultrasonic transducer to which a tool is connected; a pair of a primary power coil and a secondary power coil, which are disposed between the main body side and the tool side on a concentric axis with a rotating central axis of the tool side, wherein a drive power is supplied via the primary and secondary power coils (56a, 56b) from the power supply unit on the main body side to the ultrasonic transducer on the tool side, a pair of signal coils (58a, 58b) are disposed between the main body side and the tool side such that the signal coils (58a, 58b) are located on a concentric axis with the power coils (56a, 56b), respectively on the main body side and the tool side, a detection means (144, 172) is provided on the tool side for detecting a state of vibration of the ultrasonic transducer, and a detection signal from the detection means (144, 172) is transmittable via the signal coils (58a, 58b) from the tool side to the main body side, a power supply control means (140, 136) is provided on the main body side for controlling a power supply frequency to the primary power coil based on the detection signal from the detection means (144, 172), being characterized in that: the signal coils (58a, 58b), which are located on the concentric axis with the power coils (56a, 56b), respectively on the main body side and the tool side, are stacked with the power coils (56a, 56b) in an axial direction, and at least one of the signal coils (58a, 58b) on the main body side and the tool side, is provided with a coil winding path (68, 70, 194) including a first winding portion and a second winding portion that are wound in mutually opposite directions so that the coil winding path (68, 70, 194) generates mutually reverse electromotive forces in order to offset the electromotive forces generated in that signal coil (58a, 58b) due to an effect of a magnetic flux produced by the power coils (56a, 56b). a main body side equipped with a power supply unit that outputs AC voltage; a tool side rotatable in relation to the main body side and equipped with an ultrasonic transducer to which a tool is connected; a pair of a primary power coil and a secondary power coil, which are disposed between the main body side and the tool side on a concentric axis with a rotating central axis of the tool side, wherein a drive power is supplied via the primary and secondary power coils (56a, 56b) from the power supply unit on the main body side to the ultrasonic transducer on the tool side, a pair of signal coils (58a, 58b) are disposed between the main body side and the tool side such that the signal coils (58a, 58b) are located on a concentric axis with the power coils (56a, 56b), respectively on the main body side and the tool side, a detection means (144, 172) is provided on the tool side for detecting a state of vibration of the ultrasonic transducer, and a detection signal from the detection means (144, 172) is transmittable via the signal coils (58a, 58b) from the tool side to the main body side, a power supply control means (140, 136) is provided on the main body side for controlling a power supply frequency to the primary power coil based on the detection signal from the detection means (144, 172), being characterized in that: the signal coils (58a, 58b), which are located on the concentric axis with the power coils (56a, 56b), respectively on the main body side and the tool side, are stacked with the power coils (56a, 56b) in an axial direction, and at least one of the signal coils (58a, 58b) on the main body side and the tool side, is provided with a coil winding path (68, 70, 194) including a first winding portion and a second winding portion that are wound in mutually opposite directions so that the coil winding path (68, 70, 194) generates mutually reverse electromotive forces in order to offset the electromotive forces generated in that signal coil (58a, 58b) due to an effect of a magnetic flux produced by the power coils (56a, 56b). the signal coils (58a, 58b), which are located on the concentric axis with the power coils (56a, 56b), respectively on the main body side and the tool side, are stacked with the power coils (56a, 56b) in an axial direction, and at least one of the signal coils (58a, 58b) on the main body side and the tool side, is provided with a coil winding path (68, 70, 194) including a first winding portion and a second winding portion that are wound in mutually opposite directions so that the coil winding path (68, 70, 194) generates mutually reverse electromotive forces in order to offset the electromotive forces generated in that signal coil (58a, 58b) due to an effect of a magnetic flux produced by the power coils (56a, 56b).