A new inorganic crystal Gd3Al2Ga3O12 is being developed. This crystal is suitable for electromagnetic calorimeters used in high energy physics experiments because the time constant of light emission is small (90 ns) and the light yield is as large as that of NaI(TI) crystals. In addition, the response of the crystal can be faster by adding doping materials. By using this crystal, we aim at developing an electromagnetic calorimeter that can distinguish neutrons from gammas. In this article, we describe how we distinguish neutrons from gammas and the results of a series of beam tests for a prototype module to evaluate the separation capability.