Transient liquid phase (TLP) bonding process of Ni using Ni–11.0 mass%P binary filler metal was simulated by using a mathematical model based on diffusion analysis. In the model, diffusion-controlled transformation was assumed, and the base metal dissolution in the early stage and the subsequent isothermal solidification stage of the TLP bonding process were simulated. The calculated width of the eutectic structure at the bonding region agreed well with the experimental result and showed the validity of the model. In order to obtain the condition to reduce isothermal solidification time, the effect of factors, such as the width of filler metal, diffusivity of solute element in Ni and partition coefficient of element, were investigated by numerical simulation. The simulation showed that isothermal solidification time remarkably decreases with increasing partition coefficient of solute element. In order to confirm the numerical prediction, the TLP bonding experiment of Ni using Cu filler metal was carried out (the partition coefficient of Cu in Ni is close to unity). The experimental result showed that Cu filler metal remarkably shortened the isothermal solidification time and showed the validity of the prediction.