1. An edge detection apparatus that is configured to execute processes by a processor, the edge detection apparatus comprising: The processor configured to provide: a target pixel detector configured to detect a target pixel value of a target pixel, the target pixel being a part of a target image taken through a lens, the target image further including a peripheral image located at a peripheral area of the target image; a peripheral pixel detector configured to detect each of a plurality of blurring pixel values respectively corresponding to a plurality of peripheral pixels, the plurality of peripheral pixels being parts of the peripheral image, the plurality of peripheral pixels being located on and within a virtual circular boundary centered on the target pixel; a target pixel converter configured to convert the target pixel value into a target pixel brightness value; a peripheral pixel converter configured to convert the plurality of blurring pixel values of the plurality of peripheral pixels, which are located within the virtual circular boundary, into a plurality of first blurring pixel brightness values, and the peripheral pixel converter configured to convert the plurality of blurring pixel values of the plurality of peripheral pixels, which are located on the virtual circular boundary, into a plurality of second blurring pixel brightness values; a weight calculator configured to calculate a plurality of weighted second blurring pixel brightness values of the plurality of second blurring pixel brightness values based on a ratio of an area that is within the virtual circular boundary for each of the plurality of second blurring pixel brightness values; an average calculator configured to calculate an average blurring brightness value by dividing a sum of the plurality of first blurring pixel brightness values and the plurality of weighted second blurring pixel brightness values by the number of the plurality of peripheral pixels; and a comparator configured to compare the target pixel brightness value and the average blurring brightness value so as to determine whether the target pixel is an edge pixel of the target image.