A seal inspection device includes: a first holder including a port surrounded by an inspection target, and a through hole connected to an outside-leak detection flow path; a second holder holding the inspection target between the first and second holders; an inspection-place sealing portion forming, into a closed space, a space where the inspection target is arranged, in cooperation with the first and second holders; a pressurization valve connecting the port to both a supply source of an inspection gas and an exhaust system; a detector for the inspection gas; a first measurement valve connecting the detector to the port; and a second measurement valve connecting the outside-leak detection flow path to the detector.