Wireless power transmission systems have been considered for implantable locomotion meters from the viewpoints of limitation of measurement time and stress on animals due to their weight. On the other hand, studies on the power receiving circuit for this system have not been conducted. In addition, although the system is intended to measure the activity of several small laboratory animals, the effects of multiple power receiving coils approaching each other have not been clarified. Therefore, we fabricated prototype transmitter and receiver for wireless power transmission and investigated the changes in coupling coefficient and voltage when several receivers are in close proximity to each other. As a result, we showed that even when multiple small laboratory animals with implanted power receiving circuits were close to each other in the system, it was possible to supply a power receiving voltage higher than the target voltage of locomotion meters.