A binary pump for a liquid chromatograph comprising: a first pump unit provided with an inlet and an outlet, the inlet of the first pump unit being connected to a container containing a liquid; a second pump unit provided separately from the first pump unit and provided with an inlet and an outlet, the inlet of the second pump unit being connected to a second container containing a liquid; an output unit configured to output a liquid to be delivered; a switching valve provided with a first liquid delivery port to which the outlet of the first pump unit is connected, a second liquid delivery port to which the outlet of the second pump unit is connected, and an output port leading to the output unit, and configured to switch to any one of the following states, a first state in which the first liquid delivery port is connected to the output port and the second liquid delivery port is not connected to any port; a second state in which the second liquid delivery port is connected to the output port and the first liquid delivery port is not connected to any port; and a third state in which both the first liquid delivery port and the second liquid delivery port are connected to the output port, and a control unit configured to prevent a liquid from flowing back toward the outlet of the second pump unit from the output port by switching the switching valve to the first state at the time of delivering liquid by only the first pump unit , and to prevent a liquid from flowing back toward the outlet of the first pump unit from the output port by switching the switching valve to the second state at the time of delivering liquid by only the second pump unit . a first pump unit provided with an inlet and an outlet, the inlet of the first pump unit being connected to a container containing a liquid; a second pump unit provided separately from the first pump unit and provided with an inlet and an outlet, the inlet of the second pump unit being connected to a second container containing a liquid; an output unit configured to output a liquid to be delivered; a switching valve provided with a first liquid delivery port to which the outlet of the first pump unit is connected, a second liquid delivery port to which the outlet of the second pump unit is connected, and an output port leading to the output unit, and configured to switch to any one of the following states, a first state in which the first liquid delivery port is connected to the output port and the second liquid delivery port is not connected to any port; a second state in which the second liquid delivery port is connected to the output port and the first liquid delivery port is not connected to any port; and a third state in which both the first liquid delivery port and the second liquid delivery port are connected to the output port, and a control unit configured to prevent a liquid from flowing back toward the outlet of the second pump unit from the output port by switching the switching valve to the first state at the time of delivering liquid by only the first pump unit , and to prevent a liquid from flowing back toward the outlet of the first pump unit from the output port by switching the switching valve to the second state at the time of delivering liquid by only the second pump unit . <EOS>