The present invention provides a node apparatus and an obstacle detection method, which do not limit transmit performance and can prevent broadcast windstorm. In each port control part (21), an input frame counter (214) counts the frame input from a port input terminal (24) and an output frame counter (218) counts the frame output from a port output terminal (25). A count value collecting part (233) collects the input frame number counted by the input frame counter (214) and the output frame number counted by the output frame counter (218) from each port control part (21) in every prescribed time period. An obstacle judge part (234) compares the sum of the collected input frame number with the sum of the collected output frame number, and judges that the node apparatus (2) has obstacle when the sum of the input frame number is larger than a value which is obtained by adding the sum of the output frame number with a prescribed positive constant.
