Packet transmission quality in a communication network is measured by transmitting a measurement packet from a packet transmission node to a packet reception node. The packet transmission node is provided with a transmission counter counting the number of packets transmitted from a packet transmission node to a packet reception node, and a measurement packet counter counting the number of measurement packets transmitted from the packet transmission node to the packet reception mode. The packet reception node is provided with a reception counter counting the number of packets received from the packet transmission node. The packet transmission node transmits a measurement packet including a transmission counter value and a measurement packet counter value, to the packet reception node which calculates the number of lost packets or a loss rate of packets on the basis of the transmission counter value, the measurement packet counter value, and a reception counter value.