PURPOSE: To obtain a compact device whose operability in use is excellent by constituting the temperature detecting member of the electronic clinical thermometer by a crystal oscillator.

CONSTITUTION: The circuit block of the electronic clinical thermometer is constituted by the following devices: the crystal oscillator 502 as a temperature sensor; a power source battery 503; an externally attached electronic part for decreasing the voltage of the battery; a timer time presetting switch 505; a switch 506 for setting the counting value of an up and down counter; a switch mechanism 507 for various operations; an oscillator circuit 508; a frequency divider 509; a counter 510 for a clock; a constant voltage circuit 511; a voltage decreasing circuit 512; a preset timer circuit 513; the up and down counter 514; a data switching circuit 515; a display decoder and driver circuit 516; and a display panel 517; A part 501 which is enclosed by the chain line is constituted by an integrated circuit.