A method of focusing a printer in which the focusing of a lens is effected in accordance with an AF curve, printing is effected at an every predetermined pitchs while the lens is being moved by predetermined pitchs each along an optical axis starting from an initial position of the lens and then a lens position is selected at which optimum focus is obtained on the basis of printed images. The printing is repeated while the predetermined pitch is sequentially being made finer, in a case where the predetermined pitch differs from a pitch corresponding to the minimum resolving power of the lens. Thus, the AF curve is compensated for on the basis of the lens position which was selected during the printing at the pitch corresponding to the aforesaid minimum resolving power. Accordingly, it is possible to select an optimum lens position with high accuracy.