An image forming method using an image forming apparatus including: a latent image carrier whose surface is driven in a sub scanning direction; a deflector which scans a beam spot reciprocally in a main scanning direction substantially perpendicular to the sub scanning direction on the surface of the latent image carrier in the use of an oscillating deflect mirror so as to form spot latent images each of which formed on a pixel; developer which develops each of the spot latent images as a pixel-dot, the method includes of: halftoning for a tone reproduction in which a halftone-dot constituted by the pixel-dot(s) is formed on a cell consisting plural pixels according to a fattening type threshold matrix, wherein a plurality of cells are contiguously arranged in the main scanning direction so as to form a plurality of contiguous locations at each of which the cells adjoin mutually in the main scanning direction, each cell includes a larger-than-four even number of pixels in the sub scanning direction, and the cells, which mutually adjoin at a particular contiguous location out of the plurality of contiguous locations, are mutually shifted by an odd number of pixel(s) in the sub scanning direction.