Based on the fireball model and the spectator-participant picture, a statistical simultaneous multifragmentation model is developed for heavy ion induced reactions, with the entrance channel characteristics taken into account. This model has the density as the only parameter and it predicts the excitation energy, the temperature, and the frgmentation cross section, etc., once the incident energy, the projectile, and the target nuclei are specified. As a first application, it has been applied to the central collision data taken at National Superconducting Cyclotron Laboratory on the {sup 40}Ar+{sup 45}Sc reaction at incident energies ranging from 35 to 115 MeV/{ital A}. The study brings out the similarity in the characteristics of high energy proton induced and medium energy heavy ion induced reactions. It is observed that with rise of bombarding energy, the onset of simultaneous multifragmentation occurs at some energy between 50 and 60 MeV/{ital A}. {copyright} {ital 1996 The American Physical Society.}