An apparatus for evaluating a response time of gas sensors, comprising: a pipe; a first gas supplier for supplying a first gas to the pipe; a second gas adding machine for adding a second gas (5a, 5b, 5c) 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 (5a, 5b, 5c), each of the gas sensor being attached to the pipe on a downstream side of an addition position of the second gas (5a, 5b, 5c) in a flow direction of the first gas, wherein the second gas adding machine comprises: a supply source (50, 53, 56) of the second gas (5a, 5b, 5c); a connecting pipe (51, 54, 57) for connecting the supply source (50, 53, 56) to the pipe; and a connecting pipe on-off valve (52, 55, 58) for opening and closing the connecting pipe (51, 54, 57), wherein the second gas (5a, 5b, 5c) is different from the first gas, further characterised in that the supply source (50, 53, 56) comprises: a supply source body (500, 530, 560) for supplying the second gas (5a, 5b, 5c); and a supply pipe (501, 531, 561) to which the second gas (5a, 5b, 5c) is supplied from the supply source body (500, 530, 560) and the connecting pipe (51, 54, 57) is connected, and wherein the supply source (500, 530, 560) is configured to be capable of forming a flow of the second gas (5a, 5b, 5c) in the supply pipe (501, 531, 561) when the connecting pipe (51, 54, 57) is closed by the connecting pipe on-off valve (52, 55, 58), and in that the apparatus is configured such that a time difference between a time point when the connecting pipe (51, 54, 57) is opened by the connecting pipe on-off valve (52, 55, 58) and a time point when the gas sensors detect components in the mixed gas of the first and second gases (3a, 5a, 5b, 5c) is acquired. a pipe; a first gas supplier for supplying a first gas to the pipe; a second gas adding machine for adding a second gas (5a, 5b, 5c) 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 (5a, 5b, 5c), each of the gas sensor being attached to the pipe on a downstream side of an addition position of the second gas (5a, 5b, 5c) in a flow direction of the first gas, wherein the second gas adding machine comprises: a supply source (50, 53, 56) of the second gas (5a, 5b, 5c); a connecting pipe (51, 54, 57) for connecting the supply source (50, 53, 56) to the pipe; and a connecting pipe on-off valve (52, 55, 58) for opening and closing the connecting pipe (51, 54, 57), wherein the second gas (5a, 5b, 5c) is different from the first gas, further characterised in that the supply source (50, 53, 56) comprises: a supply source body (500, 530, 560) for supplying the second gas (5a, 5b, 5c); and a supply pipe (501, 531, 561) to which the second gas (5a, 5b, 5c) is supplied from the supply source body (500, 530, 560) and the connecting pipe (51, 54, 57) is connected, and wherein the supply source (500, 530, 560) is configured to be capable of forming a flow of the second gas (5a, 5b, 5c) in the supply pipe (501, 531, 561) when the connecting pipe (51, 54, 57) is closed by the connecting pipe on-off valve (52, 55, 58), and in that the apparatus is configured such that a time difference between a time point when the connecting pipe (51, 54, 57) is opened by the connecting pipe on-off valve (52, 55, 58) and a time point when the gas sensors detect components in the mixed gas of the first and second gases (3a, 5a, 5b, 5c) is acquired.