An optical angle modulation measurement apparatus by a delayed self-heterodyne method, comprising: a heterodyne interferometer that is fed with laser light to be measured which is optical-angle modulated by a signal generator ; a photodetector which is configured to receive output light of the heterodyne interferometer to perform heterodyne detection; a phase demodulator that is configured to demodulate a phase of a beat signal output from the photodetector; and a temporal waveform analyzer that is configured to obtain a temporal waveform of optical angle modulation, from the phase of the beat signal, wherein the heterodyne interferometer is a Mach-Zehnder interferometer including a first optical directional coupler that branches the input laser light to be measured into two, a first optical path in which an optical frequency shifter of frequency shift fs is disposed, a second optical path having an optical delay medium with a delay time π d , and a second optical directional coupler that combines an output of the first optical path and an output of the second optical path, wherein the output light of the heterodyne interferometer is output light of the second optical directional coupler, and wherein the phase of the beat signal is expressed by the following expression: φ B t ≈ − 2 πν 0 τ d + τ d dφ t dt = − 2 πν 0 τ d + 2 πν t τ d wherein ν 0 represents the center frequency of the electric field of the output light, v(t) represents the optical frequency modulation generated by said optical frequency shifter , the first term in the middle and right sides of the expression represents a DC component determined by the center frequency of the laser to be measured and the delay time τ d of said optical delay medium , and the second term represents an alternating current component resulting from the optical frequency modulation generated by said optical frequency shifter . a heterodyne interferometer that is fed with laser light to be measured which is optical-angle modulated by a signal generator ; a photodetector which is configured to receive output light of the heterodyne interferometer to perform heterodyne detection; a phase demodulator that is configured to demodulate a phase of a beat signal output from the photodetector; and a temporal waveform analyzer that is configured to obtain a temporal waveform of optical angle modulation, from the phase of the beat signal, wherein the heterodyne interferometer is a Mach-Zehnder interferometer including a first optical directional coupler that branches the input laser light to be measured into two, a first optical path in which an optical frequency shifter of frequency shift fs is disposed, a second optical path having an optical delay medium with a delay time π d , and a second optical directional coupler that combines an output of the first optical path and an output of the second optical path, wherein the output light of the heterodyne interferometer is output light of the second optical directional coupler, and wherein the phase of the beat signal is expressed by the following expression: φ B t ≈ − 2 πν 0 τ d + τ d dφ t dt = − 2 πν 0 τ d + 2 πν t τ d wherein ν 0 represents the center frequency of the electric field of the output light, v(t) represents the optical frequency modulation generated by said optical frequency shifter , the first term in the middle and right sides of the expression represents a DC component determined by the center frequency of the laser to be measured and the delay time τ d of said optical delay medium , and the second term represents an alternating current component resulting from the optical frequency modulation generated by said optical frequency shifter . <EOS>