A quadrupole mass spectrometer for use in analyzing gas components in a test piece is made in a constitution in which resistance heating of a grid is materialized, and in which a high-accuracy analysis of the gas components is possible at a low cost while preventing the sensitivity from lowering. A quadrupole mass spectrometer is provided with a sensor section which can be detachably fitted to the test piece. Supposing that the direction of fitting the sensor section to the test piece is in an upward direction, the sensor section is provided with: a predetermined shape of supporting body which is provided at a lower end of the sensor section; an ion source which is provided on the supporting body and which has a filament and a grid for ionizing the gas; a quadrupole section which is provided on the ion source and in which four columnar electrodes are disposed at a predetermined circumferential distance from one another; and an ion detection section which is disposed on the quadrupole section and which collects predetermined ions that have passed through the quadrupole section by applying DC and AC voltages between opposite electrodes.