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.