An envelope processing apparatus inserts an enclosure into an envelope and includes a first conveyor, a first ejector, a second conveyor, a second ejector, and circuitry. The first conveyor conveys the enclosure to an enclosing position. The envelope in which the enclosure is enclosed is ejected to the first ejector. The second conveyor conveys the envelope to the enclosing position via an envelope conveyance passage extended in a substantially vertical and up-and-down direction and conveys the envelope in which the enclosure is inserted to the first ejector. The second ejector is separate from the first ejector. The enclosure is ejected to the second ejector. The circuitry controls a conveyance operation of the first conveyor and the second conveyor.