The invention relates to a self-referenced device (1) for measuring the spectral phase of a periodic signal having a frequency fp, the periodic signal being carried by an optical signal, comprising: a phase shifting means (4); a transmission means (3) for transmitting at least three optical modes of said periodic signal to the phase shifting means, said optical modes defining beats at the fp frequency; the phase shifting means (4) being capable of modifying the phase difference between the beats at the fp frequency; characterised in that the measuring means (6, 7, 8) include: photoelectric conversion means (6) for detecting the variable term at the fp frequency of the optical signal received power in order to generate an electric signal (14) corresponding to the superimposition of the optical beats at the fp frequency; electric measuring means (7, 8) for measuring the amplitude of the electric signal in order to determine the amplitude of the beats at the fp frequency.