The present invention relates to a method and a device for transmitting data by a first device in a wireless communication system that supports direct device-to-device communication, wherein one or more messages are received from multiple devices, at least one message among the one or more messages is transmitted to a second device on the basis of priority, and the priority is determined in such an order that a message having the lowest first received signal strength has the highest priority, the first received signal strength indicating the received signal strength of the one or more messages.