In this paper we present the results for cold test of a coaxial cavity, which is to be installed in an existing RF gun to consist what we call-triode type RF gun. The triode type RF gun is supposed to drastically reduce the back-bombardment of electrons inherent in conventional thermionic RF guns. The coaxial cavity design was done based on tests of a prototype cavity. The latter has revealed deviations in resonance frequency, from that of the existing RF gun main cavity, which makes application of the prototype impossible. The deviation is caused by errors in design and by change due to operational conditions, namely the temperatures of the thermionic cathode and cavity body. In order to correct the resonance frequency the coaxial cavity was redesigned. Moreover the new design provides mechanisms for adjustment of the resonance frequency by means of a gasket and demountable stub system. The cold test demonstrates that the new cavity matches the requirement for application to the triode RF gun. Copyright © 2013 by JACoW.