Provided are a method and a device for transmitting an acknowledgement/not-acknowledgement (ACK/NACK) of a terminal which is set with a plurality of serving cells. The method comprises the steps of: receiving data in a subframe n of a second serving cell; and transmitting an ACK/NACK signal for the data in a subframe n+kSCC(n) of a first serving cell connected to the subframe n of the second serving cell, wherein the first serving cell is a primary cell for the terminal to execute an initial connection establishment procedure or a connection reestablishment procedure, and uses a frequency division duplex (FDD) wireless frame, the second serving cell is a secondary cell allocated to the terminal in addition to the primary cell, and uses a time division duplex (TDD) wireless frame, and the kSCC(n) is a previously determined value.