There is provided a breath test system capable of further correctly performing a diagnosis of DOPD even if a carbon dioxide concentration in an artery is not measured, including: a breath test device a device body 51 communicably connected to the breath test device 1, the breath test device 1 including: a flow path forming member having a flow path for flowing a respiratory gas of an examinee a gas sensor having a light emitting section that emits an infrared ray to the flow path, and a light receiving section that receives an infrared ray emitted by the light emitting section and a mouthpiece connected to the flow path forming member in a state of communicating with the flow path, the device body 51 including: a measuring section 52 that measures a carbon dioxide concentration contained in an exhaled breath of an examinee, based on an electric signal outputted from the gas sensor an extracting section 60 that extracts a maximum value of the carbon dioxide concentration from a measurement result of the measuring section obtained in a period of N-times (N is an integer of 2 or more) breathing of the examinee and a display section 57 for displaying a maximum value of the carbon dioxide concentration extracted by the extracting section 60.
