His biological brother was Mikimatsu FURUKAWA (1900 - 1995), an anarchist and a bookshop keeper, who is known for 'FURUKAWA Mikimatsu sanpo (stroll),' a catalogue of antiquarian books which Tsuki no wa shorin (book shop) deals with.
実弟は月の輪書林古書目録の「古河三樹松散歩」で知られる、アナキストで書店主の古河三樹松（1900年-1995年）。