There is provided an electromagnetic field measurement apparatus capable of achieving correct and timely circuit operation detection in an area where electronic devices are mounted at high density. An electromagnetic field measurement apparatus includes: a laser light source; a polarized wave controller that linearly polarizes laser light; an optical fiber probe that has an electrooptic material or a magnetooptic material at its leading end and in which the laser light reflected at the leading end is subjected to polarization modulation in accordance with an electric field intensity or a magnetic field intensity; and an analyzer that converts the laser light reflected by the optical fiber probe into intensity modulated light. The laser light source emits time-multiplexed laser light of a plurality of wavelengths different from one another. The electromagnetic field measurement apparatus further includes: an optical circulator that outputs the laser light linearly polarized by the polarized wave controller to a multiplexer/demultiplexer and outputs the laser light input from the multiplexer/demultiplexer to the analyzer; and a multiplexer/demultiplexer that outputs the laser light to different optical fiber probes according to the wavelength of the laser light and outputs the laser light to the optical circulator.