Provided are a filter medium for a filter, which makes it possible to obtain a filter high in collection efficiency, low in pressure loss and long in filter lifetime, a method for producing the same, and a filter using the filter medium for a filter. A filter medium for a filter is used as a constituent member of a filter and composed of a wet type nonwoven fabric, wherein the filter medium for a filter has a multilayer structure of two or more layers, and there is no interface between the above-mentioned two layers.