The present invention relates to a wireless communication system, and more specifically, to a method for allowing a terminal to transmit power headroom information in a wireless communication system and a device therefor. According to one aspect of the present invention, a method for allowing a terminal, in which at least one serving cell is set, to transmit power headroom information comprises the steps of: generating said power headroom information; and transmitting the power headroom information to a base station. In this case, said power headroom information includes a first field that includes a plurality of indicators, and at least one second field that indicates a power headroom level, wherein each of the plurality of indicators is capable of indicating whether at least one said second field for at least one of each of the serving cell exists.