To share, i.e., to use, a common submarine DCDC converter for both a submarine DCDC converter for positive outputting and one for negative outputting. A submarine DCDC converter according to the present disclosure includes: a DCDC conversion circuit configured to supply a first constant current input to an input terminal from a land feeding apparatus through a first submarine cable to a first output terminal, generate a second constant current using the first constant current, and supply the generated second constant current to a second output terminal; a control circuit configured to switch a polarity of the second constant current output from the second output terminal; a first switch; and a second switch.

To share, i.e., to use, a common submarine DCDC converter for both a submarine DCDC converter for positive outputting and one for negative outputting. A submarine DCDC converter according to the present disclosure includes: a DCDC conversion circuit configured to supply a first constant current input to an input terminal from a land feeding apparatus through a first submarine cable to a first output terminal, generate a second constant current using the first constant current, and supply the generated second constant current to a second output terminal; a control circuit configured to switch a polarity of the second constant current output from the second output terminal; a first switch; and a second switch.