Using mass spectrometers, we are analyzing protein complexes and protein post-translational modifications. In the body, there is protein abundance ranging 10^6 to 10^10. They interact with other proteins, low molecular ligands, DNA, or RNA. In addition, proteins have various modification including phoshorylation, metylation, and acetylation for regulation of the function, localization, and expression levels to maintain life. Regarding them, we are developing analysis methods with high sensitivity and fidelity to apply biomarker discovery, cell signaling, and epigenetics to reveal the mechanisms of diseases.