The surface-treated calcium carbonate is disclosed which is surface-treated with an organic surface treating agent, said surface-treated calcium carbonate satisfies the particular BET specific surface area (Sw), reduced heat amount per unit specific surface area (As), average pore diameter (Dxp) at which an increased amount of mercury penetration reaches the maximum value in a method of mercury penetration, and amount of an average pore diameter [maximum value of an increased amount of mercury penetration (Dyp)/average pore diameter (Dxp)]. The surface-treated calcium carbonate of the present invention is particularly useful for resins and it not only improves adhesion of resin compositions to a subject to be adhered, but forms a rigid coating film when blended into resins.