There is provided a tungsten film forming method for forming a tungsten film on a target substrate disposed inside a chamber kept under a depressurized atmosphere and having a base film formed on a surface thereof, using a tungsten chloride gas as a tungsten raw material gas and a reducing gas for reducing the tungsten chloride gas, which includes: performing an SiH4 gas treatment with respect to the target substrate having the base film formed thereon by supplying an SiH4 gas into the chamber; and subsequently, forming the tungsten film by sequentially supplying the tungsten chloride gas and the reducing gas into the chamber while purging an interior of the chamber in the course of sequentially supplying the tungsten chloride gas and the reducing gas.