A rotation angle detection sensor includes a magnet body subjected to magnetization in an in-plane direction, a first Hall element and a second Hall element separated from each other and arranged offset to one of spaces divided by an imaginary plane including a rotation axis, and a third Hall element located in a position away from a straight line passing through the first Hall element and the second Hall element. A storage section stores a rotation angle that is related to electric signals having a phase difference therebetween, among electric signals of the first Hall element, the second Hall element, and the third Hall element. A detection section detects the electric signals of the first Hall element, the second Hall element, and the third Hall element and obtains from the storage section the rotation angle that is related to the detected electric signals.