A rotation angle detection device, comprising: a part to be detected, adapted for being attached to an object to be detected for rotation position; a magnetism collecting plate, being disposed opposed to one face of the part to be detected with one of the faces thereof facing the part to be detected such that the center thereof coincides with a rotation axis of the part to be detected; a first magnetism sensing element, being disposed on a first detection axis, the first detection axis extending in parallel to said one of the faces of the magnetism collecting plate of the magnetism collecting plate and being orthogonal to the axial direction of the rotation axis of said object to be detected, for detection of a magnetic flux component in the extending direction of the first detection axis; a second magnetism sensing element, being disposed on a second detection axis, the second detection axis crossing the first detection axis, and extending in parallel to said one of the faces of the magnetism collecting plate of said magnetism collecting plate and being orthogonal to the axial direction of said rotation axis, for detection of a magnetic flux component in the extending direction of the second detection axis; and a signal output unit for outputting a signal according to a rotation position of said object to be detected, based on a result of detection by said first magnetism sensing element and said second magnetism sensing element, wherein the first and second magnetism sensing elements are disposed at the peripheral edge of the magnetism collecting plate; and wherein said part to be detected comprises a magnet and a member formed of a magnetically conducting substance and is configured such that the magnet and the member formed of a magnetically conducting substance are arranged along a radial direction with respect to said rotation axis, the magnet and said part to be detected being connected to each other, and said part to be detected is disposed, such as to make a component of the magnetic field generated from said part to be detected extend in a radial direction with respect to said rotation axis. a part to be detected, adapted for being attached to an object to be detected for rotation position; a magnetism collecting plate, being disposed opposed to one face of the part to be detected with one of the faces thereof facing the part to be detected such that the center thereof coincides with a rotation axis of the part to be detected; a first magnetism sensing element, being disposed on a first detection axis, the first detection axis extending in parallel to said one of the faces of the magnetism collecting plate of the magnetism collecting plate and being orthogonal to the axial direction of the rotation axis of said object to be detected, for detection of a magnetic flux component in the extending direction of the first detection axis; a second magnetism sensing element, being disposed on a second detection axis, the second detection axis crossing the first detection axis, and extending in parallel to said one of the faces of the magnetism collecting plate of said magnetism collecting plate and being orthogonal to the axial direction of said rotation axis, for detection of a magnetic flux component in the extending direction of the second detection axis; and a signal output unit for outputting a signal according to a rotation position of said object to be detected, based on a result of detection by said first magnetism sensing element and said second magnetism sensing element, wherein the first and second magnetism sensing elements are disposed at the peripheral edge of the magnetism collecting plate; and wherein said part to be detected comprises a magnet and a member formed of a magnetically conducting substance and is configured such that the magnet and the member formed of a magnetically conducting substance are arranged along a radial direction with respect to said rotation axis, the magnet and said part to be detected being connected to each other, and said part to be detected is disposed, such as to make a component of the magnetic field generated from said part to be detected extend in a radial direction with respect to said rotation axis.