An odor detection system, comprising: a substance sensor comprising a sensitive membrane (11 (a to j)) to react with a substance (a to j) included in an odor of a gas in correspondence with the substance (a to j), the substance sensor being configured to detect a reaction value of the sensitive membrane (11 (a to j); an odor specifier to specify the odor of the gas based on the reaction value of the sensitive membrane (11 (a to j)), detected by the substance sensor; a reaction value calculator to calculate a reaction value corresponding to the odor specified by the odor specifier based on the reaction value of the sensitive membrane (11 (a to j)), detected by the substance sensor, wherein the reaction value corresponding to the odor specified by the odor specifier is a representative value representing a level of the reaction value of the sensitive membrane (11 (a to j)) with which the substance (a to j) reacts; a percentage calculator to calculate a percentage of the reaction value corresponding to the odor specified by the odor specifier to a total of all reaction values corresponding to the odor, calculated by the reaction value calculator; and a display to display the percentage of the reaction value corresponding to the odor, calculated by the percentage calculator, so that comparison of the percentage is enabled in the odor specified by the odor specifier, characterized in that the odor detection system further comprises: a storage to store the reaction value of the sensitive membrane (11 (a to j)), detected by the substance sensor, in correspondence with time of detection, wherein the display is configured to display the percentage of the reaction value corresponding to the odor, calculated by the percentage calculator, so that comparison of the percentage of the reaction value between different detection points is enabled, based on the reaction value of the sensitive membrane (11 (a to j)), stored in the storage, wherein the display is configured to perform comparative display of percentages of the reaction values corresponding to odors in first and second measurements for gases containing the same constituents. a substance sensor comprising a sensitive membrane (11 (a to j)) to react with a substance (a to j) included in an odor of a gas in correspondence with the substance (a to j), the substance sensor being configured to detect a reaction value of the sensitive membrane (11 (a to j); an odor specifier to specify the odor of the gas based on the reaction value of the sensitive membrane (11 (a to j)), detected by the substance sensor; a reaction value calculator to calculate a reaction value corresponding to the odor specified by the odor specifier based on the reaction value of the sensitive membrane (11 (a to j)), detected by the substance sensor, wherein the reaction value corresponding to the odor specified by the odor specifier is a representative value representing a level of the reaction value of the sensitive membrane (11 (a to j)) with which the substance (a to j) reacts; a percentage calculator to calculate a percentage of the reaction value corresponding to the odor specified by the odor specifier to a total of all reaction values corresponding to the odor, calculated by the reaction value calculator; and a display to display the percentage of the reaction value corresponding to the odor, calculated by the percentage calculator, so that comparison of the percentage is enabled in the odor specified by the odor specifier, characterized in that the odor detection system further comprises: a storage to store the reaction value of the sensitive membrane (11 (a to j)), detected by the substance sensor, in correspondence with time of detection, wherein the display is configured to display the percentage of the reaction value corresponding to the odor, calculated by the percentage calculator, so that comparison of the percentage of the reaction value between different detection points is enabled, based on the reaction value of the sensitive membrane (11 (a to j)), stored in the storage, wherein the display is configured to perform comparative display of percentages of the reaction values corresponding to odors in first and second measurements for gases containing the same constituents. a storage to store the reaction value of the sensitive membrane (11 (a to j)), detected by the substance sensor, in correspondence with time of detection, wherein the display is configured to display the percentage of the reaction value corresponding to the odor, calculated by the percentage calculator, so that comparison of the percentage of the reaction value between different detection points is enabled, based on the reaction value of the sensitive membrane (11 (a to j)), stored in the storage, wherein the display is configured to perform comparative display of percentages of the reaction values corresponding to odors in first and second measurements for gases containing the same constituents.