Dosage adjuster for syringe

A dosage adjuster for a syringe comprising:

• a dosage setting part configured to set an amount of dosage dischargeable out of a liquid medicine filled in the syringe;
• and
• a setting restriction part configured to switch between a restricted state in which change in setting of the amount of dosage set by the dosage setting part is restricted and a permissible state in which the change in the setting of the amount of dosage by the dosage setting part is permissible, wherein
• the dosage setting part comprises a setting operation part configured to rotate in a circumferential direction around a central axis of a plunger of the syringe to thereby initiate change in the setting of the amount of dosage,
• the setting restriction part comprises a restriction operation part configured to move in a moving direction in which the plunger moves forward and rearward to thereby switch between the restricted state and the permissible state, and an anti-rotation part having a cylindrical shape and fixed to the cylinder in a state where the rotation in the circumferential direction is restricted,
• the restriction operation part is integrated with the setting operation part, and is configured to be inserted into the anti-rotation part,
• interfering projections are formed on an outer surface of the outer surface of the restriction operation part,
• anti-rotation projections are formed on an inner surface of the anti-rotation part,
• the restriction operation part is configured to restrict rotation of the setting restriction part by the movement toward one side in the moving direction to cause the interfering projections and the anti-rotation projections to be engaged with each other, and permit the rotation of the setting restriction part by the movement toward another side in the moving direction to cause the interfering projections and the anti-rotation projections to be disengaged from each other.