The object of the present invention is to provide an electrospray ionization mass analysis apparatus and the method thereof provided with an ESI ion source that can be directly coupled to a micro LC. The present invention provides an electrospray ionization mass analysis apparatus characterized in that a sample solution is led into a capillary tube, and high voltage is applied to the tip of this capillary tube, thereby allowing a spray ion flow of the aforementioned solution to be generated by an electrospray ion source provided therein. The ion flow generated by this ion source is led to an ion storage type spectrometer disposed in an vacuum chamber where it is subjected to mass sweeping, and the swept ion is detected by a detector so that a mass spectrum is obtained. This electrospray ionization mass analysis apparatus is further characterized by comprising a high voltage DC power source for application of the aforementioned high voltage formed by AC voltage superimposed on the DC voltage, and a AC power source. This invention ensures stable and highly sensitive ESI ionization to be performed at a flow rate ranging from several 10 &mgr;L/min to several &mgr;L/min.