PURPOSE: To provide gas concentration measuring equipment capable of measuring gas concentration at quick response and accurately calibrating a sensor with a small amount of calibrating gas.

CONSTITUTION: When the concentration of combustion gas is measured, a control means 6 rotates a gas flow rate regulating plate 3 so as to be parallel in the lengthy direction of a sampling pipe 1a through a regulating plate driving means 4 to directly introduce a sampling gas into an oxygen concentration sensor 2. When the sensor is calibrated, the control means 6 rotates the gas flow rate regulating plate 3 so as to be vertical in the lengthy direction of the sampling pipe 1a through the regulating plate driving means 4 to shut off the sampling gas, drives a valve 5a through a valve driving circuit 5b and ejects the calibrating gas in the oxygen concentration sensor 2.