A physical quantity measuring instrument for detecting signals based on a desired physical quantity and for calculating the physical quantity by executing signal processing, the physical quantity measuring instrument comprising: a signal detecting component (211, 212, 213, 214) configured to detect a plurality of signals based on the physical quantity; a signal processing component configured to linearly combine the signals detected by the signal detecting component with coefficients that vary with time and include all the signal components based on the desired physical quantity; and an arithmetic processing component configured to calculate the physical quantity from signal data output by the signal processing component; and wherein the desired physical quantity is three components X, Y and Z of a magnetic field in a three-dimensional orthogonal coordinate system; the signal detecting component has a plurality of Hall elements formed on a silicon substrate, and a disk-shaped magnetic concentrator; the Hall elements are disposed on the circumference of the magnetic concentrator in four groups at every 90 degrees around the center of the magnetic concentrator; the first, second, third and fourth groups of the Hall elements detect signals Hx + Hz = A,-Hx + Hz = B, Hy + Hz = C and -Hy + Hz = D respectively, composed of a signal Hx based on the X component of the magnetic field, a signal Hy based on the Y component and a signal Hz based on the Z component; the signal processing component has an A/D converting component configured to convert linear combinations A + C, A + D, B + D, B + C, -A - C, -A - D, -B - D and -B - C associated with the signals A to D to a digital signal from the signals A to D from the signal detecting component; and the arithmetic processing component obtains the signals Hx, Hy and Hz based on the desired physical quantity from the digital signal acquired from the signal processing component. a signal detecting component (211, 212, 213, 214) configured to detect a plurality of signals based on the physical quantity; a signal processing component configured to linearly combine the signals detected by the signal detecting component with coefficients that vary with time and include all the signal components based on the desired physical quantity; and an arithmetic processing component configured to calculate the physical quantity from signal data output by the signal processing component; and wherein the desired physical quantity is three components X, Y and Z of a magnetic field in a three-dimensional orthogonal coordinate system; the signal detecting component has a plurality of Hall elements formed on a silicon substrate, and a disk-shaped magnetic concentrator; the Hall elements are disposed on the circumference of the magnetic concentrator in four groups at every 90 degrees around the center of the magnetic concentrator; the first, second, third and fourth groups of the Hall elements detect signals Hx + Hz = A,-Hx + Hz = B, Hy + Hz = C and -Hy + Hz = D respectively, composed of a signal Hx based on the X component of the magnetic field, a signal Hy based on the Y component and a signal Hz based on the Z component; the signal processing component has an A/D converting component configured to convert linear combinations A + C, A + D, B + D, B + C, -A - C, -A - D, -B - D and -B - C associated with the signals A to D to a digital signal from the signals A to D from the signal detecting component; and the arithmetic processing component obtains the signals Hx, Hy and Hz based on the desired physical quantity from the digital signal acquired from the signal processing component.