Envelope processing apparatus and image forming system

An envelope processing apparatus to convey an envelope to an enclosing position and enclose an enclosure on which specific information is formed at a formation position, the envelope processing apparatus comprising:

• an envelope conveyor to convey the enclosure to the enclosing position to insert the enclosure into the envelope and eject the envelope in which the enclosure has been inserted;
• a sensor to acquire, as an image, a structure of the envelope during conveyance of the envelope, and acquire at least transparent-portion information indicating a position of a transparent portion included in the structure of the envelope;
• an envelope holder to hold the envelope, which has reached the enclosing position, in a state in which the enclosure is insertable into the envelope;
• and
• control circuitry configured to output position adjustment information for adjusting a position of the envelope in a width direction of the envelope at the enclosing position or a position of the specific information in a conveyance direction of the envelope, based on relative positions between the formation position of the specific information and the position of the transparent portion.