A sensing magnet apparatus for a motor, the apparatus characterized by: a plate centrally inserted by a rotation shaft; ring-shaped sensing magnet so installed as to surface-contact an upper surface of the plate, formed at a position near to a periphery with a main magnet, and formed at a position near to a through hole with a sub magnet; and a separation prevention unit physically coupling the plate and the sensing magnet to maintain the coupled state between the plate and the sensing magnet, the sensing magnet apparatus being characterized in that: the separation prevention unit includes a first grip unit complementarily formed with both the plate and the sensing magnet, and a second grip unit formed at an opposite side of the first grip unit with both the plate and the sensing magnet, wherein the first grip unit includes a grip rib extensively formed at a periphery of the plate wherein the grip rib bent to a direction facing the ring-shaped sensing magnet and formed thereinside with an accommodation groove unit, and a fixing protrusion formed at the ring-shaped sensing magnet wherein the fixing protrusion is disposed to correspond to the grip rib to be inserted into the accommodation groove unit, wherein the second grip unit includes a bending protrusion formed on the periphery of the plate at an opposite side of a formed part of the grip rib, and a lug accommodation groove of the sensing magnet formed at a position corresponding to that of the bending protrusion for the bending protrusion to be fixed and accommodated by being bent and caulked, wherein the ring-shaped sensing magnet wraps both a front surface and a rear surface of the plate, wherein the plate surface contacts the ring-shaped sensing magnet at both the front and rear surface, and wherein the ring-shaped sensing magnet is coupled with the plate through an insert injection molding process of the ring-shaped sensing magnet. a plate centrally inserted by a rotation shaft; ring-shaped sensing magnet so installed as to surface-contact an upper surface of the plate, formed at a position near to a periphery with a main magnet, and formed at a position near to a through hole with a sub magnet; and a separation prevention unit physically coupling the plate and the sensing magnet to maintain the coupled state between the plate and the sensing magnet, the sensing magnet apparatus being characterized in that: the separation prevention unit includes a first grip unit complementarily formed with both the plate and the sensing magnet, and a second grip unit formed at an opposite side of the first grip unit with both the plate and the sensing magnet, wherein the first grip unit includes a grip rib extensively formed at a periphery of the plate wherein the grip rib bent to a direction facing the ring-shaped sensing magnet and formed thereinside with an accommodation groove unit, and a fixing protrusion formed at the ring-shaped sensing magnet wherein the fixing protrusion is disposed to correspond to the grip rib to be inserted into the accommodation groove unit, wherein the second grip unit includes a bending protrusion formed on the periphery of the plate at an opposite side of a formed part of the grip rib, and a lug accommodation groove of the sensing magnet formed at a position corresponding to that of the bending protrusion for the bending protrusion to be fixed and accommodated by being bent and caulked, wherein the ring-shaped sensing magnet wraps both a front surface and a rear surface of the plate, wherein the plate surface contacts the ring-shaped sensing magnet at both the front and rear surface, and wherein the ring-shaped sensing magnet is coupled with the plate through an insert injection molding process of the ring-shaped sensing magnet. the separation prevention unit includes a first grip unit complementarily formed with both the plate and the sensing magnet, and a second grip unit formed at an opposite side of the first grip unit with both the plate and the sensing magnet, wherein the first grip unit includes a grip rib extensively formed at a periphery of the plate wherein the grip rib bent to a direction facing the ring-shaped sensing magnet and formed thereinside with an accommodation groove unit, and a fixing protrusion formed at the ring-shaped sensing magnet wherein the fixing protrusion is disposed to correspond to the grip rib to be inserted into the accommodation groove unit, wherein the second grip unit includes a bending protrusion formed on the periphery of the plate at an opposite side of a formed part of the grip rib, and a lug accommodation groove of the sensing magnet formed at a position corresponding to that of the bending protrusion for the bending protrusion to be fixed and accommodated by being bent and caulked, wherein the ring-shaped sensing magnet wraps both a front surface and a rear surface of the plate, wherein the plate surface contacts the ring-shaped sensing magnet at both the front and rear surface, and wherein the ring-shaped sensing magnet is coupled with the plate through an insert injection molding process of the ring-shaped sensing magnet.