Abstract: The present invention can accurately detect a wavelength of a light to be detected, which is output from a source of light to be detected, without an error even if there is a change in the characteristic of a spectroscope due to an individual difference among the spectroscopes or a change in the measuring environment. The device according to the invention emits at least two reference lights (Ln, La) having different wavelengths (&lgr;n, &lgr;a) as the reference lights by reference light source. And, actual characteristic value (D) of spectroscope is calculated on the basis of detection positions (Sn, Sa) of the at least two reference lights (Ln, La) on a sensor and the known wavelengths (&lgr;n, &lgr;a) of the at least two reference lights (Ln, La) (D=(&lgr;a−&lgr;n)/(Sa−Sn)).

Abstract: A plasma arc working apparatus of water cooling type provides a circulation system for circulating cooling water through a circulation passage in order to cool a working plasma arc torch and an introduction device for introducing pressurized gas into the circulation passage in order to drain the cooling water remaining in the circulation passage forcibly therefrom when the power switch for supplying electric power to the working apparatus is switched off.