A signal processing device comprising: a plurality of sensors (1-1, 1-2, 1-3, 1-4) configured to sense physical quantities, to convert the physical quantities into electric physical quantity signals, and to output the respective electric physical quantity signals, a signal inverting unit configured to receive the electric physical quantity signals output from the plurality of sensors (1-1, 1-2, 1-3, 1-4), to convert the electric physical quantity signals into element signals, and to combine the element signals to respective combined signals (P1 to P4); a measuring unit configured to sequentially receive the combined signals output from the signal inverting unit, and to carry out processing on the received combined signals and output corresponding measured signals; and a computing unit configured to receive the measured signals from the measuring unit, and to compute signal components based on the measured signals sequentially output from the measuring unit, wherein the signal inverting unit generates each element signal either as an inverted signal in which one of the electric physical quantity signals is inverted or as a non-inverted signal in which said electric physical quantity signal is not inverted, and wherein the signal inverting unit comprises one switch (2-1, 2-2, 2-3, 2-4) for each of said sensors, each switch comprising two changeover switches (2-1A, 2-1B,...) configured to change over the contact between two input terminals receiving the electric physical quantity signal of the corresponding sensor and two output terminals outputting the corresponding element signal such as to output either said inverted signal or said non-inverted signal and wherein the outputs of the switches (2-1 to 2-4) are connected in series to serially combine the selectively inverted or non-inverted electric physical quantity signals so as to generate the respective combined signals (P1 to P4). a plurality of sensors (1-1, 1-2, 1-3, 1-4) configured to sense physical quantities, to convert the physical quantities into electric physical quantity signals, and to output the respective electric physical quantity signals, a signal inverting unit configured to receive the electric physical quantity signals output from the plurality of sensors (1-1, 1-2, 1-3, 1-4), to convert the electric physical quantity signals into element signals, and to combine the element signals to respective combined signals (P1 to P4); a measuring unit configured to sequentially receive the combined signals output from the signal inverting unit, and to carry out processing on the received combined signals and output corresponding measured signals; and a computing unit configured to receive the measured signals from the measuring unit, and to compute signal components based on the measured signals sequentially output from the measuring unit, wherein the signal inverting unit generates each element signal either as an inverted signal in which one of the electric physical quantity signals is inverted or as a non-inverted signal in which said electric physical quantity signal is not inverted, and wherein the signal inverting unit comprises one switch (2-1, 2-2, 2-3, 2-4) for each of said sensors, each switch comprising two changeover switches (2-1A, 2-1B,...) configured to change over the contact between two input terminals receiving the electric physical quantity signal of the corresponding sensor and two output terminals outputting the corresponding element signal such as to output either said inverted signal or said non-inverted signal and wherein the outputs of the switches (2-1 to 2-4) are connected in series to serially combine the selectively inverted or non-inverted electric physical quantity signals so as to generate the respective combined signals (P1 to P4).