Beam monitor system and particle beam irradiation system

A beam monitor system having a simple configuration for improving a measurement precision specifying a position and the width. A beam monitor system, comprising collection electrodes that include a plurality of groups each having a plurality of adj acent wire electrodes, and detect an ionized particle beam passing therethrough, a first signal processing device that sets one wire electrode in the groups of the collection electrodes as a typical wire electrode, receives a detection signal output from the typical wire electrode to process the signal and a beam monitor controller (8b) that obtains a beam position of the ionized particle beam that has passed through the wire electrodes on the basis of a processed signal from the first signal processing device.