A digital phase‐sensitive detector for a modified Bruker electron‐spin‐resonance (ESR) spectrometer, equipped with an Aspect 2000 minicomputer is described. Magnetic field modulation is derived from a clock in the computer, which makes it possible to perform the data acquisition fully synchronously with the modulation. The resulting high phase accuracy makes it possible to compress the data to a single modulation period before the Fourier transformation. Both the in‐phase and the phase‐quadrature signals (of the first or second harmonic) are recorded simultaneously. The system is so efficient that the data processing including the Fourier transformation is approximately 1000 times faster than a previously reported digital phase‐sensitive detector system for ESR [T. Watanabeetal., Appl. Spectrosc.34, 456 (1980)].