An ion generation apparatus 10 comprises: an arc chamber 50; a magnetic field generator 52 that generates a magnetic field B to be applied in the axial direction in an internal space S of the arc chamber 50; a first cathode cap 72 that protrudes toward the inside of the arc chamber 50 in the axial direction and emits thermal electrons toward the internal space S; and a first thermal shield 76 that includes a first extension portion which axially extends in a tubular shape on the radially outer side of the first cathode cap 72 and which is adjacent to the first cathode cap 72 with a gap interposed therebetween in the radial direction perpendicular to the axial direction, a first tip portion that protrudes toward the inside of the arc chamber, and a first tip opening that opens in the axial direction in the first tip portion. The first tip opening has a first opening width in the radial direction smaller than the maximum width of the first cathode cap 72 in the radial direction.