PROBLEM TO BE SOLVED: To provide a technique that allows COPD (Chronic Obstructive Pulmonary Disease) to be more accurately diagnosed without measuring carbon dioxide concentration in arterial blood.SOLUTION: A breath-testing system 100 is provided that comprises: a breath-testing device 1； and a device main body 51 communicably connected to the breath-testing device 1. The breath-testing device 1 comprises: a flow channel formation member that has a flow channel for flowing respiratory air of a subject； a gas sensor that has a light emitting unit emitting IR to the flow channel, and a light reception unit receiving the IR emitted from the light emitting unit； and a mouth piece that is connected to the flow channel formation member while being communicated with the flow channel. The device main body 51 comprises: a measurement unit 52 that measures carbon dioxide concentration contained in exhalation of the subject on the basis of an electric signal output from the gas sensor； an extraction unit 60 that extracts a maximum value of the carbon dioxide concentration from a measurement result obtained during a period while the subject respires N (N is an integer equal to or more than 2) times, of the measurement unit； and a display part 57 for displaying the maximum value of the carbon dioxide concentration extracted by the extraction unit 60.SELECTED DRAWING: Figure 1【課題】動脈血中の二酸化濃度を測定しなくても、ＣＯＰＤの診断をより正確に行うことができる技術を提供する。【解決手段】呼気検査装置１と、呼気検査装置１に通信可能に接続される装置本体５１と、を備える呼気検査システム１００である。呼気検査装置１は、被検者の呼吸気を流すための流路を有する流路形成部材と、流路に赤外線を出射する発光部、および、発光部が出射した赤外線を受光する受光部を有するガスセンサと、流路に連通する状態で流路形成部材に接続されるマウスピースと、を備える。装置本体５１は、ガスセンサから出力される電気信号を基に、被検者の呼気に含まれる二酸化炭素濃度を計測する計測部５２と、被検者がＮ回（Ｎは２以上の整数）呼吸する期間に得られる計測部の計測結果から二酸化炭素濃度の最大値を抽出する抽出部６０と、抽出部６０で抽出した二酸化炭素濃度の最大値を表示するための表示部５７と、を備える。【選択図】図１
