A liquid feeding apparatus comprising: a pump unit which has a primary side pump and a secondary side pump configured to perform suction and discharge of liquid by driving a distal end of a plunger (10, 32) in one direction in a pump chamber (4, 24), an outlet part of the primary side pump and an inlet part of the secondary side pump being connected to each other via a check valve; a primary side pressure sensor which detects the pressure inside the pump chamber of the primary side pump; a secondary side pressure sensor which detects the pressure inside the pump chamber of the secondary side pump; a drive control unit which controls operation of the primary side pump and the secondary side pump to perform a suction operation of the secondary side pump during the discharge operation of the primary side pump and to perform a suction operation of the primary side pump during the discharge operation of the secondary side pump; and a preloading operation unit which acquires a signal of the primary side pressure sensor and a signal of the secondary side pressure sensor after the suction operation of the primary side pump is terminated and before the discharge operation of the secondary side pump is terminated, and executes a preloading operation of driving the primary side pump to the discharge side, until the pressure inside the pump chamber of the primary side pump becomes substantially equal to the pressure inside the pump chamber of the secondary side pump, on the basis of an acquired signal; characterized in that: the liquid feeding apparatus further comprises a preloading time determining unit which determines a time allocated to the preloading operation, on the basis of a preset liquid feeding flow rate, and in that the preloading operation unit is configured to acquire the signal from the primary side pressure sensor and the secondary side pressure sensor at an acquisition frequency determined depending on the preloading time determined by the preloading time determining unit. a pump unit which has a primary side pump and a secondary side pump configured to perform suction and discharge of liquid by driving a distal end of a plunger (10, 32) in one direction in a pump chamber (4, 24), an outlet part of the primary side pump and an inlet part of the secondary side pump being connected to each other via a check valve; a primary side pressure sensor which detects the pressure inside the pump chamber of the primary side pump; a secondary side pressure sensor which detects the pressure inside the pump chamber of the secondary side pump; a drive control unit which controls operation of the primary side pump and the secondary side pump to perform a suction operation of the secondary side pump during the discharge operation of the primary side pump and to perform a suction operation of the primary side pump during the discharge operation of the secondary side pump; and a preloading operation unit which acquires a signal of the primary side pressure sensor and a signal of the secondary side pressure sensor after the suction operation of the primary side pump is terminated and before the discharge operation of the secondary side pump is terminated, and executes a preloading operation of driving the primary side pump to the discharge side, until the pressure inside the pump chamber of the primary side pump becomes substantially equal to the pressure inside the pump chamber of the secondary side pump, on the basis of an acquired signal; characterized in that: the liquid feeding apparatus further comprises a preloading time determining unit which determines a time allocated to the preloading operation, on the basis of a preset liquid feeding flow rate, and in that the preloading operation unit is configured to acquire the signal from the primary side pressure sensor and the secondary side pressure sensor at an acquisition frequency determined depending on the preloading time determined by the preloading time determining unit. the liquid feeding apparatus further comprises a preloading time determining unit which determines a time allocated to the preloading operation, on the basis of a preset liquid feeding flow rate, and in that the preloading operation unit is configured to acquire the signal from the primary side pressure sensor and the secondary side pressure sensor at an acquisition frequency determined depending on the preloading time determined by the preloading time determining unit.