In a model editing apparatus, a model transformation function transforms SM (source model) 0 into TM (target model) 0, and generates TDM (transformation dependency model) 0. Moreover, when an SM editor generates SM1 by updating SM0, the model transformation function transforms SM1 into TM1 and generates TDM1. When a TM editor generates TM0_n by editing TM0 independently of the change in SM0, a Change element registration function registers a difference Δ2 between TM0 and TM0_n in TDM0, thereby generating TDM0_n. Then, in response to a call, a merge function merges a difference Δ1 between TDM0 and TDM1 extracted by a Δ1 extraction function, and a difference Δ2 extracted from TDM0_n, according to prestored processing patterns.