A pedal operation amount detection apparatus (10; 60) including an operation pedal apparatus that includes a transmitting member (18; 92) transmitting a depression operation force, and an output member to which the depressing operation force is transmitted from the transmitting member (18; 92) and to which a reaction force corresponding to the depressing operation force is applied, the pedal operation amount detection apparatus (10; 60) further including a sensor member (30; 62) disposed on a load transmission path of the transmitting member (18; 92) and deformed by the depressing operation force and the reaction force and the pedal operation amount detection apparatus (10; 60) electrically detecting deformation of the sensor member (30; 62), wherein the sensor member (30; 62) is an elongate member that is torsionally and elastically deformable about a torsion center line in a longitudinal direction and is disposed at a position offset from the transmitting member (18; 92) in a direction parallel to a support axis about which the transmitting member is pivotable; one of an operation input portion at which the depressing operation force is applied to the sensor member (30; 62) and a reaction force acting portion at which the reaction force is applied to the sensor member (30; 62) is set at a position apart from the torsion center line in a direction parallel to the support axis; and the operation input portion and the reaction force acting portion are set at positions offset from each other in a direction parallel to the support axis; wherein the transmitting member (18; 92) is a plate member having a flat portion perpendicular to the support axis, and is disposed so as to be pivotable about the support axis or an axis parallel to the support axis; the sensor member (30; 62) is disposed parallel to a side face of the flat portion of the transmitting member (18; 92); the pedal operation amount detection apparatus characterized in that it is further provided with a cylindrical member that is fixedly fitted to an intermediate portion of the sensor member (30; 62) in the longitudinal direction so as to protrude in a direction perpendicular to the torsion center line S and parallel to the support axis, the cylindrical member being inserted in a through-hole formed in the transmitting member (18; 92) with a play, a bushing (50; 110; 112; 114; 116) through which a coupling pin is passed, the bushing concentrically and fixedly fitted to an inner side of a portion of the cylindrical member, the portion protruding from the sensor member (30; 62), and a pair of support pins (32; 34) fixedly fitted to the transmitting member so as to protrude toward the sensor member (30; 62) parallel to the cylindrical member, and inserted in a pair of support holes (36; 38) formed at respective end portions of the sensor member (30; 62) in the longitudinal direction to be relatively rotatable and to support the sensor member (30; 62); and one of a contact portion at which one of the support pins (32; 34) and the corresponding support hole (36; 38) contact each other and a contact portion at which the bushing (50; 110; 112; 114; 116) and the coupling pin contact each other serves as the operation input portion, and the other serves as the reaction force acting portion.