In a transmission device, a signal processing circuit generates an aggregate physical layer convergence protocol data unit (A-PPDU) by adding a guard interval to each of a first part of a first physical layer convergence protocol data unit (PPDU) transmitted over each of a first through L'th channel of a predetermined channel bandwidth, where L is an integer of 2 or greater, a second part of the first PPDU transmitted over each of an (L+1)'th through P'th channel, which is a variable channel bandwidth that is N times the predetermined channel bandwidth, where N is an integer of 2 or greater and P is an integer of L+1 or greater, and a second PPDU transmitted over the (L+1)'th through P'th channel. A wireless circuit transmits the A-PPDU.