A packet processing apparatus includes a packet buffer unit that temporarily holds packet data, a packet processing unit that processes packet data output from the packet buffer unit, a clock supply unit that supplies a clock signal to the packet processing unit, and a control unit that detects a buffer vacant time indicating a time during which no packet data exists in the packet buffer unit based on an accumulation amount of the packet data in the packet buffer unit, and controls an operational state of the clock supply unit in accordance with the buffer vacant time.