Apparatus and method for evaluating response time of gas sensor

An apparatus for evaluating a response time of gas sensors includes: a pipe; a first gas supplier for supplying a first gas to the pipe; a second gas adding machine for adding a second gas to the first gas in the pipe; and gas sensors for detecting components in a mixed gas of the first gas and the second gas, each of the gas sensors being attached to the pipe on a downstream side of an addition position of the second gas in a flow direction of the first gas. The second gas adding machine includes: a supply source of the second gas; a connecting pipe for connecting the supply source to the pipe; and a connecting pipe on-off valve for opening and closing the connecting pipe.