In Japan, the tax support system for nonprofit organizations was legislated in 2001, then significantly revised in 2011. Behind these events was constant lobbying by a social movement organization called C's. This paper examines how C's used two types of lobbying tactics: outside and inside. As outside tactics, the organization carried out “conflict expansion” by appealing to mass media and collecting signatures, and “signaling” by holding campaigns with Diet members. As inside tactics, it presented petitions to the government and attended political party hearings. These tactics were scheduled over one year and were repeated 12 years. Although the frequency of the outside tactics decreased, the organization constantly employed its inside tactics. After the change in government, C's changed the political situation and achieved its goal.