An object of the present invention is to provide a rotational angle detection apparatus and a power steering apparatus capable of detecting a rotational angle of a rotational shaft eve when a failure has occurred in a magnetic detection portion. One aspect of the present invention is a rotational angle detection apparatus including a first magnetic detection portion provided on a rotational axis and configured to detect a change in a magnitude or a direction of a magnetic field, and a second magnetic detection portion provided on the rotational axis and disposed at a position offset from the first magnetic detection portion in a direction along the rotational axis. The second magnetic detection portion is configured to detect the change in the magnitude or the direction of the magnetic field. The rotational angle detection apparatus further includes a magnet provided on an outer side in a radial direction of the rotational axis with respect to the first magnetic detection portion and the second magnetic detection portion and disposed in such a manner that an N-pole and an S-pole face each other around the rotational axis. The magnet is provided rotatably relative to the first magnetic detection portion and the second magnetic detection portion. The rotational angle detection apparatus is configured to detect a rotational angle of the magnet relative to the first magnetic detection portion and the second magnetic detection portion based on signals output from the first magnetic detection portion and the second magnetic detection portion.