To analyze water and steam positively by installing a cooling device in a blowdown system connected to the upper stream part of a sampling cooler in a device for sampling water and steam in a power plant system to analyze pH, dissolved oxygen, conductivity, silica, and the like.

Water sampled from a sampling position in a certain sampling cycle enters a sampling cooler 17 from a sample inlet through a shut-off valve V1, and after being cooling in the sampling cooler 17, the water is depressurized by a depressurizing device 18, and its temperature is detected by a temperature fuse 19. A valve V3 is then opened to inject the water successively in ion exchange resin 21, a thermostatic layer 22, a flow meter 23 and an electric conductivity meter 24 to recover the sample water. In this case, a blowdown system is diverged from a prior stage of the sampling cooler 17, and blowdown water and steam are cooled in a blowdown cooler 29 so as to prevent the failure of the thermostatic layer 22 and the like caused by blowdown water and steam of high temperature and high pressure passing a sampling system.