An enclosing device includes an envelope conveyance path, an envelope loader, an envelope-position restrictor, and an envelope-position adjuster. The envelope conveyance path conveys an envelope to an enclosing position at which an enclosure is enclosed into the envelope. The envelope loader loads the envelope to be supplied to the envelope conveyance path. The envelope-position restrictor restricts a loaded position of the envelope in the envelope loader. The envelope-position adjuster adjusts a position of the envelope with respect to a conveyance direction of the envelope while maintaining a state in which the envelope-position restrictor restricts the loaded position of the envelope.