To provide a highly sensitive and accurate thermal conductivity sensor capable of expanding a measurement range for measuring physical quantities such as a vacuum degree, a gas flow rate, and a liquid flor rate.

The thermal conductivity sensor comprises a heater and a temperature sensor mounted on a thin film separated from a substrate by heat, integrates an output from a temperature sensor by time in a little-noise cooling process after stopping the heating of a heater, and defines it as an output. A high-temperature first integration output and a low-temperature second integration output that are time integration outputs under two different temperatures after stopping the heating are integrated by time or simultaneously integrated so as to correct ambient temperature using a difference integration value thereof and, when needed, information of an absolute value of a substrate and information of the first integration output value. The thermal conductivity sensor may be applied to a hydrogen gas sensor and an absolute humidity sensor. A preferred sensor chip therefor is also provided.