An authentication system for detecting breath alcohol, comprising: a breath introduction unit that breath of a person is introduced into; an imaging unit that is configured to capture images of the face of a person blowing breath on the breath introduction unit ; a breath detection unit that is configured to detect breath components containing an alcohol component contained in the introduced breath from the breath introduction unit ; an imaging control unit that is configured to control the imaging unit ; a breath analysis unit that is configured to analyze the alcohol component of the breath detected by the breath detection unit ; and an image analysis unit that is configured to analyze the images captured by the imaging unit , wherein the imaging control unit has a function of controlling the imaging unit to perform - a first image capturing during the introduction of the breath into the breath introduction unit , and - a second image capturing after an analysis of the breath components in the breath analysis unit ; and the image analysis unit has a function of outputting a result as to whether or not a person of the images in the first image capturing and a person of the image in the second image capturing are the same person, and the breath introduction unit and the breath detection unit are configured to be mounted on a portable terminal accommodated in a portable housing and provided with the imaging unit or accommodated in the same housing as the portable terminal provided with the imaging unit , characterized in that the breath detection unit includes a saturated water vapor detection element for detecting whether or not the introduced breath is saturated water vapor and has a sufficient introduction volume, and the first image capturing is started when an output value of the saturated water vapor detection element exceeds a predetermined threshold. a breath introduction unit that breath of a person is introduced into; an imaging unit that is configured to capture images of the face of a person blowing breath on the breath introduction unit ; a breath detection unit that is configured to detect breath components containing an alcohol component contained in the introduced breath from the breath introduction unit ; an imaging control unit that is configured to control the imaging unit ; a breath analysis unit that is configured to analyze the alcohol component of the breath detected by the breath detection unit ; and an image analysis unit that is configured to analyze the images captured by the imaging unit , wherein the imaging control unit has a function of controlling the imaging unit to perform - a first image capturing during the introduction of the breath into the breath introduction unit , and - a second image capturing after an analysis of the breath components in the breath analysis unit ; and - a first image capturing during the introduction of the breath into the breath introduction unit , and - a second image capturing after an analysis of the breath components in the breath analysis unit ; and the image analysis unit has a function of outputting a result as to whether or not a person of the images in the first image capturing and a person of the image in the second image capturing are the same person, and the breath introduction unit and the breath detection unit are configured to be mounted on a portable terminal accommodated in a portable housing and provided with the imaging unit or accommodated in the same housing as the portable terminal provided with the imaging unit , characterized in that the breath detection unit includes a saturated water vapor detection element for detecting whether or not the introduced breath is saturated water vapor and has a sufficient introduction volume, and the first image capturing is started when an output value of the saturated water vapor detection element exceeds a predetermined threshold. <EOS>