PURPOSE: To moisten or apply a glue on the flap of an envelope while avoiding the end of the flap, and perform the sealing of an envelope with a favorable finish by setting a timing to drive a sealing material applying apparatus by detecting the edge of the envelope being carried in.

CONSTITUTION: When the front end of an envelope, being carried in on a carrying path 2, facing sideways, at a specified speed, reaches a carry-in sensor 3, a brush driving solenoid 5 is turned on after a specified period of time from that point by a control circuit 14, and a brush 4 is lowered. Then, when the rear end of the envelope reaches the carry-in sensor 3, the brush driving solenoid is turned off after a specified period of time from that point by the control circuit 14, and the brush 4 is raised. While the brush 4 is lowered, a glue or water is applied on the flap of the envelope being carried at the specified speed, facing sideways. Then, the envelope is closed at a flap close unit 11, and the sealing is completed at sealing rollers 12.