It is an object to prevent impersonation in breath measurement by using a portable device. After breath is introduced into a breath introduction inlet 11 of a breath introduction device 1, a first image group is acquired by continuously capturing images over a predetermined period, and after drinking determination based on the introduced breath from the breath introduction inlet 11, the portable device is provided with an imaging device 11 that acquires a second image by capturing an image again and outputs whether or not each image in the first image group and the second image are the images of the same person.