A study of internal centrifugal blower is very interest in case problems for improve the characteristics. Also, the form of volute tongue which have an affects to characteristics centrifugal blower. This paper is described about effect of tongue shape for characteristics of centrifugal blower. Visualized experiment and numerical calculation for the tongue shape of 3 types clarified the flow characteristic of the flow near the tongue in centrifugal blower. As the results, the following facts are made clear. The behavior of the flow near the tongue agrees with that obsessed by flow visualization experiments. Numbly the stagnation punt moves around the tongue when changing the mass flow.