To provide an irradiation window capable of reducing the amount of charged particle lost by impinging on the side walls of holes in a perforation grid plate, preventing lowering of heat conduction performance of the perforation grid plate and sufficiently cooling window foil.

This irradiation window 4a is contacted by thinning the thickness of a hole forming region 9 more inside than the periphery of a perforation grid plate 6 and laying a plurality of cooling pipes 24 along the surface of the hole forming region 9. Furthermore by connecting each cooling pipe 24 to a coolant path 10 in the periphery of the perforation grid plate 6, the flow of coolant 12 in the cooling pipes 24 is allowed.