from the outer circumferential surface of the chamber is removed furthermore because a state in which the axial direction of the chamber lies in the horizontal direction is established when a liquid coinjector such as this is located for example above the bed of the patient contact with the body of the patient resulting in change in the position of the valve body is unlikely to occur moreover provided it is tubular and extends in the axial direction a chamber of any shape for example a cylinder square cylinder triangular cylinder elliptical cylinder or a semi circular cylinder shape may be used in addition a valve body formed by cutting away of part of a columnar body for the purpose of closing just one of a pair of branch tubes and in which a flow passage configured as a hole formed in the interior of the columnar body can be used as the valve body in addition the liquid coinjector pertaining to at least one embodiment of the present invention is further characterized by provision in an outer circumferential surface of the valve body of a first groove part by which one main branch tube of the pair of main branch tubes and the confluent branch part communicate and a second groove part by which the other.