Abstract: An optical power measuring apparatus for measuring a power level of an optical signal comprised of a light intensity modulated signal, received by a light receiving element is provided. In the apparatus, a first signal path including a first voltage detection circuit and a first amplifier circuit supplies a processor with a first signal having a voltage proportional to a current flowing through a light receiving element (PD), and a second path including a TIA, a DC detection circuit and a second amplifier circuit supply the processor with a second signal. The second signal corresponding to an envelope of a voltage from the TIA.