u03b4 u03b4 0 con u03b8 where u03b4 0 is the emission efficiency when the primary electron beam strikes perpendicular to the target of the secondary electron emission section 107 which is dependent on the energy of the primary electron beam and the material of the secondary electron emission section in this embodiment metal is used as the material of the irradiation surface of the secondary electron emission section 107 in other words as the target the secondary electron emission efficiency of metal is at a maximum of u03b4 1 3 when the energy of the primary electron beam is 800 ev if the primary electron beam is made to strike at an angle to the target of the secondary electron emission section 107 the emission efficiency can be increased in this embodiment the irradiation angle u03b8 of the primary beam is 40 u00b0 the secondary electrons emitted from the secondary electron emission section 107 are accelerated by the voltage v t from the bias application power source 120 or the voltage from the voltage application power source 121 and are extracted into an energy distribution section by the electric field of the extraction electrode 109 a voltage of 10 v is applied in the secondary electron emission section 107 and a voltage of 200 v is applied in the extraction electrode 109 in this case the shielding electrode 108 is used to adjust the field distribution at the end portion of the extraction electrode 109 to relieve the field the high energy components of the accelerated secondary electrons are removed by the parallel flat plate energy analyzers 110 and 111.