A bulk ink supply system of an inkjet printer includes a connector, an ink flow path, and an on-off valve. The connector is attachable to and detachable from an ink container. The connector includes an ink guiding path formed in the connector. The ink flow path connects the ink guiding path and an inkjet head of the inkjet printer to supply an ink from the ink guiding path to the inkjet head. The on-off valve allows communication between the ink guiding path and the ink flow path when the ink container is attached to the connector and hinders communication between the ink guiding path and the ink flow path when the ink container is detached from the connector.