To judge whether it is dry or not accurately, and at the same time, prevent flowmeter measurement error from increasing due to erroneous judgment.

When a flow rate is measured, switches S1 and S2 are opened as in the figure and electromotive force generated at electrodes 5 and 6 is amplified as a flow-rate signal. At this time, when the entire electrode is exposed due to the dry condition, the flow-rate signal increases indefinitely as shown in Figure b. In a dry judgment mode, the switches S1 and S2 are closed. Electromotive force generated at the electrodes 5 and 6 is short-circuited by resistors R1 and R2, and especially a flow-rate signal V decreases as shown in Figure c. When the value becomes lower than a constant value V0 stored by a ROM 16, a microprocessor 14 judges that it is dry.