A toner consumption calculator includes a plurality of line memories; a processor that sequentially records image data including a plurality of pixels into the line memories and processes the image data by sequentially reading the image data from the line memories; an exposing unit that performs exposure in accordance with the processed image data and forms a latent image based on the image data on an image carrier; and a counter that sequentially reads the image data from the line memories and counts toner consumption of a target pixel on the basis of light amounts of surrounding pixels of the target pixel. The processor reads the image data from the line memories L times (L is a natural number) and reads M pixels (M is a natural number) per line memory and per clock. M is equal to or larger than the number of surrounding pixels of the target pixel in a main-scanning direction. The counter reads the image data from the line memories L times, reads the M pixels per line memory and per clock, and counts the toner consumption of N target pixels (N ≤ M).