PURPOSE: To prevent consumption of an undetected sample and to enable longtime detection by making a sample heating speed be continuously variable with the amount of ions proportional to the vaporizing and evaporating amount of a sample.

CONSTITUTION: Ion beams 2 generated and accelerated in an ion source 1 are provided with mass spectrography by a magnetic field 3, and only a flow of specific ions focuses and passes through a collector slit 8 and reaches an ion collector 9. A signal detected in an ion collector 9 is amplified into an appropriate value by an amplifier 10 and next sent to a memorizing . processing .displaying device such as a CPU 11. A sample 4 is heated by a heater 6 housed in a pipette 5 and vaporized/evaporated to enter an ion source 1. The heater 6 is energized by a heating power source 7. A constant-speed heating system where the heating power is normally increased gradually at a constant rate is employed as a heating system in this case. Thus, a vapor pressure of the sample does not attain to its level which is a detectable limit in the device, and the sample is not consumed while it is undetected. Hence, failures to detection and measurement of the sample, caused by too fast or too slow heating of the sample, can be prevented.