PURPOSE: To make pH measurement accurate and easy, by supplying a sample including an insoluble material with high temperature into an insoluble material removing tank, and supplying the sample to a pH meter under the cooled state.

CONSTITUTION: A partitioning plate 6 is provided between two partitioning plates 4 and 5 in a removable lid 7, and an insoluble-material removing tank 3 is constituted. A sample, which is cooled to some extent, is supplied to the tank 3 through a sample cooling pipe 1. The insoluble material floating in the tank 3 is made to overflow and is removed through a line 8. The sample is supplied to a pH meter 10 through a line 9. Thus the maintenance of the apparatus is made easy.