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A microbeam system was installed at Dynamitron laboratory at Tohoku University and is applicable to simultaneous in-air/in-vacuum PIXE, RBS, SE, and STIM analyses, and 3D µ-CT. Insufficient beam brightness of the source and field contamination of the microbeam line restricted spatial resolution. In order to improve the performance of Tohoku microbeam system, optimization and modification of the ion source and microbeam system were performed. By the modification of the system, the beam brightness of the system was increased to 1.0 pA·µm-2·mrad-2·MeV-1 at the half divergence of 0.2 mrad. Considering the brightness and the magnification, obtainable target current will be 200 and 900 pA for beam spot sizes of 1.0 × 1.0 and 2.0 × 2.0 µm2, respectively. The modification of the source meets both the lifetime and the performance. The parasitic field contamination of the system was reduced down to less than 0.5 % by replacing the beam scanner chamber and a part of beam duct. Both resolution and beam currents are sufficient for our applications of in-air/in-vacuum PIXE, RBS, SE, and STIM analyses and 3D PIXE-µ-CT. [ABSTRACT FROM AUTHOR]