an object of the present invention is to provide means for solving troubles . examples of the troubles include sensitivity degradation and resolution degradation of a mass spectrometer , which are caused by an axis deviation of a component , particularly at least one orifice located between an ion source and a detector , to decrease the number of ions reaching the detector , and a variation in performance caused by exchange of components such as the orifice . for example , the invention has the following configuration in order to solve the troubles . a mass spectrometer includes : an ion source ; a detector that detects an ion ; an orifice and a mass separator that are disposed between the ion source and the detector ; and an axis adjusting mechanism that adjusts axis positions of the orifice and / or the mass separator such that an opening of the orifice and / or an incident port of the mass separator is disposed on a line connecting the ion source and an incident port of the detector .