Power transmission device and power transmission-reception system

A power transmission-reception system, comprising:

• a power transmission device;
• and
• a power reception device, wherein
• the power transmission device comprises:
• a power transmission unit configured to perform wireless power transmission;
• a communication unit configured to perform wireless communication within a range wider than a power transmission possible range of the power transmission unit;
• and
• a power transmission control circuit configured to control the power of wireless power transmission of the power transmission unit, wherein
• the power transmission control circuit controls the power of wireless power transmission of the power transmission unit according to a number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than a threshold when the power transmission unit performs power transmission by first power, and a number of power reception devices for which the communication unit received a response indicating that power reception is performed from power reception devices receiving power equal to or more than the threshold when the power transmission unit does not perform power transmission or performs power transmission by second power smaller than the first power, and
• the power reception device has a communication unit transmitting to the power transmission device an indication of receiving power when power equal to or more than the threshold is received.