In liquid-feeding sections for feeding two types of mobile phases A, B, respectively, actual flow rate measuring sections capable of detecting back-flows are provided in downstream of liquid-feeding pumps, respectively. Control devices control driving of the liquid feeding pumps, respectively, so that measured flow rates by the actual flow rate measuring sections correspond to set flow rates on the liquid-feeding flow paths, respectively. In a case where the set flow rate is zero, when either of the actual flow rate measuring sections detects the back-flow, the corresponding liquid-feeding pump is driven so as to prevent the back-flow.