To make more of a silane compound adhere on the pigment powder surface than by conventional methods.

A silane compound represented by formula (1): (RCnH2n)aSi(OCmH2m+1)b, a metal salt and a pigment powder are mixed and dispersed in a mixed solvent of a 1-4C alcohol and water to surface treat the pigment powder with the silane compound, wherein R is a 3-21C hydrocarbon, a polyether group or a perfluoroalkyl group; the groups may have a functional group such as an amino group or a hydroxyl group in the chain length, have a straight chain or branched chain, and may have a single chain length or a multiple chain length; n is an integer of 1 to 12, and m is an integer of 1 to 3; and a and b are each an integer of 1 to 3, and a+b=4.