An image processor includes a luminance signal processor configured to execute an amplification by utilizing a gain set by a plurality of gain step-sizes including a first gain step-size and a second gain step-size less than the first gain step-size, to an image signal component which is equal to or less than a fixed luminance level in an image signal. The control circuit is configured to control increase and decrease of the gain utilized by the amplification and the gain step-sizes based on a ratio that a luminance level of the image signal component is equal to or less than the reference detection level, a ratio that the luminance level of the image signal component is equal to or less than a first detection level greater than the reference detection level, and a ratio that luminance level of the image signal component is equal to or less than a second detection level less than the reference detection level.