The present invention provides a cartridge type double seal having a size small enough to be mounted on the outer surface of an apparatus without using a space in a stuffing box and without requiring any special design and modification. In a seal device (1), a seal case (44) is fixed and installed by the set screw (18), screwed in radially inside from the far end of the mounting groove (15) of the seal cover (10) through the screw groove (17), at the innermost end of the seal cover (10). The thickness of thickness direction can be reduced because the seal case (44) is not axially supported and fixed.