Human body communication (HBC) is a wireless transmission method that utilizes the human body as part of the transmission medium. In HBC, a high-frequency signal is transmitted by a current flowing through the body surface and via the near-field electric field around it. Due to the lack of specific equipment and tools to measure HBC transmission characteristics, HBC systems are still in the development stage. In this study, a multilayered arm phantom and suitable measurement devices are proposed to measure the transmission efficiency between a 10-MHz transmitter worn on the wrist and a receiver in contact with the palm. Measurements with a real human subject were also performed. Additionally, numerical models for calculating the transmission efficiencies are introduced to validate the measurements. The transmission efficiencies obtained from the measurements using the phantom and from the simulation using the numerical model were in a reasonable agreement; however, the results of the measurements using the phantom and the subject differed, which we attributed to the effect of the body trunk.