To prevent scatter of foreign matters such as peeling steam oxidation scale in steam piping to a turbine and wear damage of the turbine in a thermal electric power plant or the like.

Sound wave detecting devices detecting collision sound of foreign matters in piping are arranged on piping and attachment metal fittings provided on the piping in the piping communicating a boiler and a steam turbine in the thermal electric power plant or the like. For example, as shown in figure 1, an AE sensor 26 as a sound wave measuring device, an AE tester 27, an X-Y recorder 28 are arranged on a high temperature reheat steam drain temperature measurement seat 25 arranged on a high temperature reheat steam drain piping 23. Since sound generated when the foreign matters accompanied with steam flow collides against an inner wall of the piping or the attachment metal fitting of a temperature measuring apparatus or the like is detected, scatter of the foreign matter to the turbine is prevented and wear damage of the turbine is prevented by supplying steam to the turbine after it is confirmed that no foreign matter scatters.