A pedal operation amount detecting device that is provided in an operating pedal apparatus including a transmitting member having a pedal arm of an operating pedal that is arranged so as to be pivotable about a support axis and that is depressed, and an output member to which a depression force is transmitted from the transmitting member and to which a reaction force corresponding to the depression force is applied, the pedal operation amount detecting device including a sensor member that is arranged on a load transmission path at a position offset from the transmitting member in a direction parallel to the support axis and that is deformed by the depression force and the reaction force, and the pedal operation amount detecting device electrically detecting a deformation of the sensor member.