A transmitter, a communication system, and a communication method capable of realizing communication of more than a set bandwidth with respect to a packet communication with a bandwidth guarantee set therefore by using a set bandwidth as the minimum guaranteed bandwidth, wherein when a transmitter transmits packet data, it decides whether or not packet communication guarantees a bandwidth based on a guaranteed bandwidth set in advance, and adds a first identifier to the packet data when guaranteeing bandwidth, and adds a second identifier when not guaranteeing the bandwidth.