In the transport sector, Plug-in Hybrid Electric Vehicle (PHEV) is being developed as an environmentally friendly vehicle. The electric energy of PHEVs is charged mainly during nighttime when the electricity price is low. Therefore, we have proposed a charging power control of PHEVs to compensate the Load Frequency Control (LFC) capacity in the nighttime. In this study, we propose a control method based on Area Control Error (ACE) and frequency characteristic of PHEV KPHEV, which is a change in charging power divided by a change in frequency. ACE is a required adjustment in generation to keep the balance of supply-and-demand; hence, we can also keep the balance by adjusting the demand as much as ACE. LFC signal fLFC calculated by the following equation fLFC = -ACE/ KPHEV is dispersed to all PHEVs; then, PHEVs control the charging power on the basis of fLFC. We evaluated the proposed control method by using an interconnected 2-area model and obtained the following results. Charging power control based on the proposed method can effectively suppress tie-line flow deviation and frequency deviation, and it could substitute for LFC capacity.