In January 2011, magmatic eruptions at Shinmoe-dake, Kirishima, Japan, started for the first time in 300 years. After three sub-plinian explosive events, lava accumulation started at the summit crater. The accumulation lasted for about three months, and the final volume of the accumulated lava reached 1.5 x 10(7) m(3). We conducted aeromagnetic surveys using an unmanned autonomous helicopter over the Shinmoe-dake summit crater in late May 2011, and late October to early November, 2011, in order to investigate the magnetization of this area and changes in the magnetic field associated with the 2011 eruption. The averaged magnetization intensity around Shinmoe-dake is 1.5 A/m. A demagnetized area elongated in the north to northwest direction from Shinmoe-dake has been detected. We also detected a clear change in the total magnetic field between the two aeromagnetic observations characterized by positive and negative changes in the south and north, respectively, of the Shinmoe-dake edifice. These changes are well reproduced by a model in which 20-70% of lava accumulated in the summit crater was cooled down below the Curie temperature and has been magnetized.