A semiconductor device manufacturing method includes: forming a core pattern on a foundation film, the core pattern containing a material generating acid by light exposure; selectively exposing part of the core pattern except an longitudinal end portion; supplying a mask material onto the foundation film so as to cover the core pattern, the mask material being crosslinkable upon supply acid from the core pattern; etching back the mask material to expose an upper surface of the core pattern and remove a portion of the mask material formed on the end portion of the core pattern, thereby leaving a mask material side wall portion formed on a side wall of the core pattern; and removing the core pattern and processing the foundation film by using the mask material sidewall portion left on the foundation film as a mask.