There is a pedal operation amount detecting device provided in an operating pedal apparatus that includes: a transmitting member including 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 includes a sensor member, which is arranged on a load transmission path of the transmitting member and which is deformed by the depression force and the reaction force, and the pedal operation amount detecting device electrically detects a deformation of the sensor member. The pedal operation amount detecting device is suggested as a device that detects a depression force or a depression stroke of for example, a brake pedal for a service brake, a brake pedal for a parking brake, an accelerator pedal or a clutch pedal of a vehicle. A device described in Patent Document 1 is an example of the above-described device. An operating rod 26 corresponds to the output member, a clevis 28 corresponds to the transmitting member, and a rod-like member 40 corresponds to the sensor member.