PURPOSE: To easily and reliably measure the water content in a solid body by supplying the water content generated when the solid sample is heated into a moisture sensor together with carrier gas and measuring the water content by this sensor.

CONSTITUTION: Moisture sensors 2 and 9 are stored in a water content measuring cell 3 where a carrier gas flow passage 4 for inert gas is connected. Then a container 6 where the solid sample is replaceable is provided in the middle of the flow passage 4 and heated by a tape heater 7. When the solid sample in the container 6 is heated by the tape heater 7, the water content in the solid sample vaporizes in the gap in the container. This vapor is supplied into the water content measuring cell 3 with gaseous argon supplied from a gaseous argon cylinder 5 and dehumidified by a dehumidifier 8. The measured value of the moisture sensor 2 in the measuring cell 3 is compared with the standard oscillation frequency output of a cell 10 for comparison. A frequency counter 12 detects frequency variation from the result of said comparison and a display part 13 displays the corresponding water amount or frequency.