An electron beam irradiation apparatus in a partial vacuum method is structured with a static pressure floating pad 18 connected to a vacuum chamber 14 containing an electron beam column 15 and in a condition that the static pressure floating pad 18 is attached to a subject 1 to be irradiated without contacting, and an electron beam irradiating the subject 1 to be irradiated through an electron beam path 19 of the static pressure floating pad 18, whereby the vacuum chamber and the electron beam column can be maintained in the required degree of vacuum even in a condition that the static pressure floating pad 18 is separated from the subject 1 to be irradiated. A vacuum seal valve 30 including a piston to open and close the electron beam path 19 is provided within the static pressure floating pad 18. When the static pressure floating pad 18 is separated from the subject 1, the vacuum seal valve 30 is structured to be activated to close the electron beam path 19 so as to prevent the air from flowing into the vacuum chamber 14. In this structure, the vacuum seal valve 30 is formed with a round shaped cross section and in a tapered shape with a narrow tip so as to accomplish high vacuum seal without a gap, so that the degree of vacuum in the vacuum chamber and the electron beam column can surely be maintained.