PURPOSE: To find the temperature distribution in a substance on-line, by obtaining the temperature distribution based on a peak position where an ultrasonic wave reaches, a propagating time required for reception, data of a thickness and surface temperature of a body whose temperature is to be measured, and data of a position where the ultrasonic wave arrives when the inner temperature is uniform.

CONSTITUTION: A slant angle probe 101 is placed on the surface of a body 1 whose temperature is to be measured and excited by an exciting part 102. Ultrasonic waves are periodically oscillated. The signal is received by an array probe 103 and inputted to an ultrasonic-wave input-point operating part 105. Then the receiving position on the array probe 103 is obtained. A temperature operating part 106 analyzes the temperature distribution in the body 1 whose temperature is to be measured based on the output data of the position and the time from the ultrasonic-wave input-point operating part 105, the thickness data and the surface temperature data from a thickness gage and a surface thermometer, and the data of the position where the ultrasonic wave arrives when the inner temperature is uniform.