A no-electric field region (246A) and an electric field region (246B) are formed in a flight tube (246). In the no-electric field region (246A), ions introduced from an ion emission unit fly. In the electric field region (246B), a reflectron (244) is provided and the ions having passed through the no-electric field region (246A) are reflected to the no-electric field region (246A) by an action of an electric field formed on an inner side of a plurality of electrodes (244A, 244B). A through-hole (246D) is formed in at least a part of the flight tube (246) to be closer to the electric field region (246B) than the no-electric field region (246A).