the present invention relates to an operation mode switching apparatus comprising a structure for making it possible to minimize the waste of energy caused by troubles occurring in optical fiber lines and the like in order to efficiently utilize the energy consumed in an optical transmission system aimed for a long - term operation ; a raman amplifier including the operation mode switching apparatus ; and an optical transmission system including the raman amplifier . if an optical fiber line acting as an optical transmission medium breaks in the optical transmission system , the signal power detected from the optical fiber decreases , whereby it changes to a set value or less or the amount of decrease in signal power per unit time changes by a set value or more . the operation mode switching apparatus comprises a control section for monitoring such a change in signal power , thereby switching the pumping light supply operation from a communication mode to a wait mode for minimizing the waste of pumping energy in response to the occurrence of troubles .