To apply a vibration to a band S in a plurality of vibration modes, and correctly obtain a tension of the band S.

A tension detector 9 applies the vibration to the band S suspended and spaced in a noncontact state, and includes: a plurality of vibration applying means 4 provided in the width direction of the band S; a vibration mode selecting means 7 for selecting the vibration mode generated in the band S; a vibration application control means 8 for controlling one of the vibration applying means 4 among a plurality of the vibration applying means 4 for applying the vibration to the band S in response to the vibration mode selected by the vibration mode selecting means 7; a displacement detecting means 5 for measuring a displacement in the vertical direction of the band S vibrated by a noncontact vibration applying apparatus 1 at a plurality of locations in the width direction of the band S; and a tension detecting section 10 for obtaining a vibration waveform of the band S from the displacement of the band S measured by the displacement detecting means 5, and detecting the tension of the band S from an eigenfrequency of the obtained vibration waveform.