An excitation operation brake comprising: a braking shaft serving as a braking target member; an armature attached to the braking shaft such that the armature rotates integrally with the braking shaft; a field core including a disc facing the armature in an axial direction of the braking shaft, and an annular groove; and an exciting coil stored in the annular groove of the field core, wherein the disc forms a magnetic flux path that makes a magnetic flux generated by energizing the exciting coil flow in a radial direction of the disc, the disc includes a plurality of magnetic shielding portions (47, 48) that make the magnetic flux bypass to the armature a plurality of times, and of the plurality of magnetic shielding portions (47, 48), an outer magnetic shielding portion located on an outer side in the radial direction includes a bypass magnetic path having a magnetic resistance smaller than a magnetic resistance of a magnetic path that bypasses the armature, characterized in that the outer magnetic shielding portion includes a plurality of outer slits formed at a first interval in a circumferential direction of the disc, and outer bridge portions that are regions between the outer slits adjacent in the circumferential direction, wherein the outer slits have a width smaller than a width of the outer bridge portions in the circumferential direction, the outer bridge portions form the bypass magnetic path, the plurality of magnetic shielding portions (47, 48) further includes an inner magnetic shielding portion located on an inner side in the radial direction with respect to the outer magnetic shielding portion, the inner magnetic shielding portion includes a plurality of inner slits formed at a second interval in the circumferential direction, and inner bridge portions that are regions between the inner slits adjacent in the circumferential direction, the inner slits have a width larger than a width of the inner bridge portions in the circumferential direction, the armature includes an outer armature facing the outer magnetic shielding portion, and an inner armature facing the inner magnetic shielding portion, the outer armature and the inner armature are supported by a disc-shaped support member that rotates integrally with the braking shaft, the outer armature, the inner armature, and the support member form an armature assembly (3, 81), and the armature assembly (3, 81) is biased toward the disc by a spring member. a braking shaft serving as a braking target member; an armature attached to the braking shaft such that the armature rotates integrally with the braking shaft; a field core including a disc facing the armature in an axial direction of the braking shaft, and an annular groove; and an exciting coil stored in the annular groove of the field core, wherein the disc forms a magnetic flux path that makes a magnetic flux generated by energizing the exciting coil flow in a radial direction of the disc, the disc includes a plurality of magnetic shielding portions (47, 48) that make the magnetic flux bypass to the armature a plurality of times, and of the plurality of magnetic shielding portions (47, 48), an outer magnetic shielding portion located on an outer side in the radial direction includes a bypass magnetic path having a magnetic resistance smaller than a magnetic resistance of a magnetic path that bypasses the armature, characterized in that the outer magnetic shielding portion includes a plurality of outer slits formed at a first interval in a circumferential direction of the disc, and outer bridge portions that are regions between the outer slits adjacent in the circumferential direction, wherein the outer slits have a width smaller than a width of the outer bridge portions in the circumferential direction, the outer bridge portions form the bypass magnetic path, the plurality of magnetic shielding portions (47, 48) further includes an inner magnetic shielding portion located on an inner side in the radial direction with respect to the outer magnetic shielding portion, the inner magnetic shielding portion includes a plurality of inner slits formed at a second interval in the circumferential direction, and inner bridge portions that are regions between the inner slits adjacent in the circumferential direction, the inner slits have a width larger than a width of the inner bridge portions in the circumferential direction, the armature includes an outer armature facing the outer magnetic shielding portion, and an inner armature facing the inner magnetic shielding portion, the outer armature and the inner armature are supported by a disc-shaped support member that rotates integrally with the braking shaft, the outer armature, the inner armature, and the support member form an armature assembly (3, 81), and the armature assembly (3, 81) is biased toward the disc by a spring member.