The electron beam ion source (Kobe EBIS) has been developed to perform modification of surfaces using highly charged ions (HCIs). Recent study revealed that periodic intermission of electron beam improves charge state distribution of extracted ions. The repetition of ON/OFF of electron beam with the period in the order of 100ms and the width of beam-off time being 1ms or less made it possible to produce Ar¹⁵⁺ to Ar¹⁷⁺ effectively, while the charge is limited less than 14+ under the ordinary operation mode. A spike of HCIs is also produced at each moment of electron beam off.