A semiconductor strain sensor including a plurality of Wheatstone bridges formed on a main surface of a single-crystal silicon substrate by impurity diffusion resistors, each of the plurality of Wheatstone bridges being adapted to detect a difference between a strain quantity generated in an x-axial direction and a strain quantity generated in a y-axial direction, the main surface of the single-crystal silicon substrate being a face of single-crystal silicon and the x-axial direction and the y-axial direction corresponding to a <110> direction of the single-crystal silicon substrate and being perpendicular to each other on the main surface of the semiconductor substrate, and an adder circuit for adding output voltage values of the plurality of Wheatstone bridges such as to provide an added difference between the strain quantities generated in the x-axial direction and the strain quantities generated in the y-axial direction as a detection result, wherein each of the plurality of Wheatstone bridges includes four diffusion resistors providing current in the <110> direction and constituted by two P-type diffusion resistors having a longitudinal direction in the y-axial direction and arranged in a direction of causing current to flow parallel to the y axis as a first y-axial-direction resistor and a second y-axial-direction resistor, and by two P-type diffusion resistor having a longitudinal direction in the x-axial direction and arranged in a direction of causing current to flow parallel to the x axis as a first x-axial-direction resistor and a second x-axial-direction resistor, wherein the impurity diffusion resistors constituting the plurality of Wheatstone bridges have equal widths and lengths and respective first and second y-axial direction and x-axial direction resistors of the plurality of Wheatstone bridges are arranged adjacent to each other at a shorter interval than their length, so that output signal components of the plurality of Wheatstone bridges increase with equal sensitivities in accordance with an average strain quantity in a region to be measured. a plurality of Wheatstone bridges formed on a main surface of a single-crystal silicon substrate by impurity diffusion resistors, each of the plurality of Wheatstone bridges being adapted to detect a difference between a strain quantity generated in an x-axial direction and a strain quantity generated in a y-axial direction, the main surface of the single-crystal silicon substrate being a face of single-crystal silicon and the x-axial direction and the y-axial direction corresponding to a <110> direction of the single-crystal silicon substrate and being perpendicular to each other on the main surface of the semiconductor substrate, and an adder circuit for adding output voltage values of the plurality of Wheatstone bridges such as to provide an added difference between the strain quantities generated in the x-axial direction and the strain quantities generated in the y-axial direction as a detection result, wherein each of the plurality of Wheatstone bridges includes four diffusion resistors providing current in the <110> direction and constituted by two P-type diffusion resistors having a longitudinal direction in the y-axial direction and arranged in a direction of causing current to flow parallel to the y axis as a first y-axial-direction resistor and a second y-axial-direction resistor, and by two P-type diffusion resistor having a longitudinal direction in the x-axial direction and arranged in a direction of causing current to flow parallel to the x axis as a first x-axial-direction resistor and a second x-axial-direction resistor, wherein the impurity diffusion resistors constituting the plurality of Wheatstone bridges have equal widths and lengths and respective first and second y-axial direction and x-axial direction resistors of the plurality of Wheatstone bridges are arranged adjacent to each other at a shorter interval than their length, so that output signal components of the plurality of Wheatstone bridges increase with equal sensitivities in accordance with an average strain quantity in a region to be measured.