Various surroundings factor damages boiler tube. We must inspect tubes and find the damage which lead to hazard before hazard happened. In boiler tube, the most typical damage is thickness reduction. We show Inner Ultrasonic Testing method with examples of inspecting thickness reduction for boiler tube. We developed the probe which have multi-channel and can inspect cross section of tube at one time. Inner Ultrasonic Testing method is that we apply Ultrasonic Testing for boiler tube by the probe in boiler tube.The probe have enabled that inspection speed of twin-boiled water tubes and multi-bend tubes is rapidly. Because of the probe is available electrical revolution which is speedier than mechanical that.In addition we can inspect drawn parts by creating dedicated tool which modify the angle of sensor along inside wall of tube.