A current detector for a bidirectional switching power supply , wherein the current detector is able to detect a current flowing through a detection resistor provided between a low-side switching element (SW2) contained in the bidirectional switching power supply which selectively performs step-down operation and step-up operation, and a reference potential point, the current detector for a bidirectional switching power supply comprising: an inverting amplifier circuit for inversely amplifying a current signal relating to temporal change of current flowing through the detection resistor (Rs), and outputting the same as an inversely amplified signal; a non-inverting amplifier circuit for non-inversely amplifying the current signal relating to temporal change of current flowing through the detection resistor (Rs), and outputting the same as a non-inversely amplified signal; an OR circuit for mathematically processing each input of the inversely amplified signal and the non-inversely amplified signal by logical sum and outputting a mathematically processed signal, wherein the OR circuit outputs forward signal components of the inputted inversely amplified signal and non-inversely amplified signal as the mathematically processed signal; and a detection circuit for detecting a value of current flowing through the detection resistor from the mathematically processed signal, wherein the detection circuit is configured to detect the current value obtained from the mathematically processed signal to be inputted in a former half period of bisected halves of an ON period of the switching element (SW2) when step-down operation is performed, and is configured to detect the current value obtained from the mathematically processed signal to be inputted in a latter half period of bisected halves of the ON period of the switching element (SW2) when step-up operation is performed. an inverting amplifier circuit for inversely amplifying a current signal relating to temporal change of current flowing through the detection resistor (Rs), and outputting the same as an inversely amplified signal; a non-inverting amplifier circuit for non-inversely amplifying the current signal relating to temporal change of current flowing through the detection resistor (Rs), and outputting the same as a non-inversely amplified signal; an OR circuit for mathematically processing each input of the inversely amplified signal and the non-inversely amplified signal by logical sum and outputting a mathematically processed signal, wherein the OR circuit outputs forward signal components of the inputted inversely amplified signal and non-inversely amplified signal as the mathematically processed signal; and a detection circuit for detecting a value of current flowing through the detection resistor from the mathematically processed signal, wherein the detection circuit is configured to detect the current value obtained from the mathematically processed signal to be inputted in a former half period of bisected halves of an ON period of the switching element (SW2) when step-down operation is performed, and is configured to detect the current value obtained from the mathematically processed signal to be inputted in a latter half period of bisected halves of the ON period of the switching element (SW2) when step-up operation is performed. <EOS>