According to various embodiments, disclosed are a method by which a terminal simultaneously transmits messages in at least two carriers in a wireless communication system supporting device to device (D2D) communication, and an apparatus therefor. Particularly, disclosed are a method by which a terminal simultaneously transmits messages in at least two carriers, and an apparatus therefor, the method comprising the steps of: independently sensing, by a carrier, a transmission resource, and calculating the ratio of transmission resources, which can be simultaneously transmitted on at least two carriers, on the basis of a result of the sensing by the carrier; setting the sensed transmittable transmission resource as a transmission candidate resource when the calculated transmission resource ratio is greater than or equal to a preset threshold ratio; and selecting a transmission resource to be used for the message transmission in each of at least two carriers within the transmission candidate resource.