An apparatus and method for generating femtosecond electron beam are disclosed. The apparatus for generating electron beam by discharging an electron generated via a cathode to an anode includes a transmission window provided at one side of the cathode to allow incident laser to pass therethrough, a pinhole formed on the anode such that the pinhole corresponds to the position of the electron generated from the transmission window, and a focusing unit provided at one side of the cathode and generating an electric field to accelerate and at the same time concentrate the electron to the pinhole. Electrons are simultaneously concentrated and accelerated to the pinhole by an electric field generated by the focusing unit positioned at the cathode to generate femtosecond electron beam.