A vacuum bulb comprising fixed and movable electrodes in a vacuum container, each of said fixed and movable electrodes having an arc electrode and an electrode rod of a highly conductive metal supporting the arc electrode, said arc electrode being made, at its entire surface facing another arc electrode, of an alloy containing a refractory metal and a highly conductive metal, said electrode rod having a rear conductor smaller in diameter than the arc electrode and an external connecting conductor larger in diameter than the rear conductor, said arc electrode and said electrode rod being integrally formed by means of diffusion bonding of solid phase, said fixed and movable electrodes being each provided in the surfaces mutually facing each other with a plurality of grooves formed from an inside to an outside of each electrode, each groove passing through the arc electrode.