In the solar flare observed on June 3, 2012, high energy gamma-rays and neutrons were observed. The event includes a remarkable feature of a high neutron/gamma-ratio in the secondary particles. We have examined whether this high n/$gamma$-ratio can be explained by simulation. As a result of simulations using the GEANT4 program, the high n/$gamma$-ratio may be reproduced for the case that helium and other heavy ions were dominantly accelerated in the flare.