A luminance signal processing apparatus that detects an average luminance level, adaptively to various video signal formats. This luminance signal processing apparatus includes a window pulse generation unit 101 for generating a window pulse signal S110 that indicates a period during which a luminance signal of an input video signal is sampled; a luminance value addition unit 102 for obtaining a total sum of luminance values of the luminance signal in the period indicated by the window pulse signal S110; a number-of-pixel addition unit 103 for obtaining the number of pixels in the period indicated by the window pulse signal S110; a bit shift unit 104 for bit-shifting an output signal of the luminance value addition unit 102 and an output signal of the number-of-pixel addition unit 103, respectively; and a division unit 105 for dividing the bit-shifted output signal of the luminance value addition unit 102 by the bit-shifted output signal of the number-of-pixel addition unit 103, thereby obtaining an average luminance level.