To provide a pipe flow monitoring apparatus and a pipe flow monitoring method which monitor changes in a flow even for a part a conventional flowmeter was unable to deal with for such reasons as being a large-diameter pipe, a large flow, and a large drift.

The pipe flow monitoring apparatus 200 includes: three or more ultrasonic transmitting/receiving units 250 for measuring the flow rate information of one point using ultrasonic waves from different positions; a flow rate combination unit 220 for calculating a three-dimensional flow rate value from the three or more pieces of flow rate information; an initial condition acquisition unit 222 for acquiring an initial condition from a three-dimensional flow rate value at one point in time; a progressed condition acquisition unit 224 for acquiring a progressed condition from a three-dimensional flow rate value at an optional point in time; and a change acquisition unit 226 for acquiring a relative change by comparing the progressed condition to the initial condition.