A conveyance mechanism is provided. A bag body processing unit is installed with a roller unit. While the process transfer unit transfers a bag body processing unit from a first guide station to a second guide station, the roller unit moves from a first guide surface to a second guide surface and is placed on the second guide surface in the second guide station. In the second guide station, the roller unit is placed on the second guide surface, and a second guide part is moved from a first variation position to a second variation position while the roller unit is placed on the second guide surface, so that the roller unit is moved from a first height position to a second height position.