The present invention relates to vaccine conjugates composed of a hapten linked to a carrier compound, which are used for active or passive immunization in order to elicit antibodies against the hapten. The circumferential surface of the transfer roller aside from the concave portion makes contact with the image bearing member due to rotation of the transfer roller while the rotational axis of the transfer roller moves away from the image bearing member. A guide portion is provided in the retainer which is flexibly deformed by interference from the provisional locking projection and the final locking projection, and a locked portion is formed, which is a locking hole opened in the guide portion. The adjustable connection means can be a variable length actuator whose length determines the stroke of the pan or sieve.