a liquid container detachably mountable to a container holder , the container holder includes a container body for containing liquid and including a front side engaging portion and a rear side engaging portion for engagement with the container holder , the front side engaging portion and rear side engaging portion being disposed at a leading side and a trailing side , respectively with respect to an inserting direction of the container into the container holder ; and a projection , provided on only one of lateral sides of the container body which extend parallel with the inserting direction , for being guided , when the container is mounted to the container holder , along an upper end of a guide wall provided in the container holder while the other lateral side is being limited by an inner surface of the container holder , and the container is being rotated substantially about the front side engaging portion .