A surge current detection device detachably attached to a conductor, the surge current detection device detecting a surge current entering the conductor, the surge current detection device comprising: a holder (40;40A) releasably holding the conductor; a magnetic force concentrating member including a magnetic material, the magnetic force concentrating member being mounted in the holder (40;40A), removably receiving the conductor, and concentrating a magnetic flux included in a magnetic field generated by the surge current entering the conductor to a high density at a predetermined detection region; and a magnetic material sheet mounted on the holder (40;40A) in such a manner that the magnetic material sheet is positioned at the detection region, the magnetic material sheet detecting the surge current, wherein that the magnetic material sheet includes a sheet member including a front surface and a back surface, the back surface side being disposed at the detection region, a recording layer provided on the front surface side of the sheet member, the recording layer including a plurality of microcapsules each including a magnetic powder (72a1), whose state of orientation changes depending on the concentrated magnetic flux, encapsulated in a floating state in a liquid (72a2), the recording layer being capable of recording and erasing a state of entrance of the surge current therein and therefrom, and a light transmissive protection film covering the recording layer and allowing a state of the recording and the erasure in the recording layer to be viewed from an outside the magnetic force concentrating member includes the magnetic material having a plate-like shape having a substantially U-shaped cross-section, the magnetic material removably receiving the conductor; the detection region includes a region in a vicinity of an area between open ends of the substantially U-shaped magnetic material the holder (40,40A) has a first holder body (40-1,40A-1) and a second holder body (40-2,40A-2) with which the substantially pipe-like component was divided into two in the state of opening and closing freedom in the direction of longish side, a through hole (44, 45) for griping the conductor to expandable/contractable is formed in the both ends of the first holder body (40-1,40A-1) and the second holder body (40-2,40A-2), respectively, the magnetic force concentrating member is mounted inside the first holder body (40-1,40A-1); and the magnetic material sheet is mounted by the second holder body (40-2,40A-2) in the state which can be viewed from an outside. a holder (40;40A) releasably holding the conductor; a magnetic force concentrating member including a magnetic material, the magnetic force concentrating member being mounted in the holder (40;40A), removably receiving the conductor, and concentrating a magnetic flux included in a magnetic field generated by the surge current entering the conductor to a high density at a predetermined detection region; and a magnetic material sheet mounted on the holder (40;40A) in such a manner that the magnetic material sheet is positioned at the detection region, the magnetic material sheet detecting the surge current, wherein that the magnetic material sheet includes a sheet member including a front surface and a back surface, the back surface side being disposed at the detection region, a recording layer provided on the front surface side of the sheet member, the recording layer including a plurality of microcapsules each including a magnetic powder (72a1), whose state of orientation changes depending on the concentrated magnetic flux, encapsulated in a floating state in a liquid (72a2), the recording layer being capable of recording and erasing a state of entrance of the surge current therein and therefrom, and a light transmissive protection film covering the recording layer and allowing a state of the recording and the erasure in the recording layer to be viewed from an outside the magnetic force concentrating member includes the magnetic material having a plate-like shape having a substantially U-shaped cross-section, the magnetic material removably receiving the conductor; the detection region includes a region in a vicinity of an area between open ends of the substantially U-shaped magnetic material the holder (40,40A) has a first holder body (40-1,40A-1) and a second holder body (40-2,40A-2) with which the substantially pipe-like component was divided into two in the state of opening and closing freedom in the direction of longish side, a through hole (44, 45) for griping the conductor to expandable/contractable is formed in the both ends of the first holder body (40-1,40A-1) and the second holder body (40-2,40A-2), respectively, the magnetic force concentrating member is mounted inside the first holder body (40-1,40A-1); and the magnetic material sheet is mounted by the second holder body (40-2,40A-2) in the state which can be viewed from an outside. the magnetic material sheet is mounted by the second holder body (40-2,40A-2) in the state which can be viewed from an outside.