In this study, a time-of-flight mass spectrometer is developed to analyze the mass-to-charge ratio of ion beams generated from an electron beam ion source (EBIS) at the RAON heavy ion accelerator facility. The time-of-flight mass spectrometer comprises a Bradbury–Nielson gate, steerer, mirror electrode, and microchannel plate detector. The Bradbury–Nielson gate is applied to generate a bunch beam with a 5-ns pulse width at the front end of the time-of-flight system. A double-stage reflector is employed to obtain a beam chromatic correction from the energy spread of the ion beam generated from the EBIS. The design is created through optics simulation using the SIMION code, with 133Cs as the reference ion. Consequently, the charge state of 27+ separated from neighboring states at a maximum voltage of 20 kV is obtained. By utilizing ion sources of Cs1+ (m/z 133) and Rb1+ (m/z 85 and m/z 87) to perform the performance test on the designed TOFMS system, the spectral peak of the ion sources and a relatively high mass resolution are obtained. This paper introduces the development process and test results of the time-of-flight mass spectrometer in detail.