PROBLEM TO BE SOLVED: To provide a rotation angle detection device that highly accurately calculates a rotation angle at reference timing when a rotation angle sensor element or AD converter fails in the rotation angle detection device for calculating a rotation angle on the basis of signals from a plurality of redundantly provided rotation angle sensor elements.SOLUTION: AD converters 41 and 42 of a rotation angle detection device 501 are configured to acquire a cos signal and sin signal analogically output in accordance with a rotation angle of a detection object by a plurality of rotation angle sensor elements 31, 32 and 33, and sequentially convert the analog signals into a cos signal value and sin signal value serving as a digital value at a fixed conversion cycle. An angle calculation processing unit 51 is configured to calculate a plurality of angles substitutable when the rotation angle sensor element or AD converter fails, in which calculation of the angle is conducted based on the cos value and sin value converted at one or a plurality of conversion timing becoming symmetrical in front of and at the back of a center in a time axis when reference timing is defined as the center in the time axis, and further relative conversion timing of the cos value and sin value to be used for calculation is different.SELECTED DRAWING: Figure 2

【課題】冗長的に設けられた複数の回転角センサ素子からの信号に基づいて回転角を算出する回転角検出装置において、回転角センサ素子又はＡＤ変換器の故障時に、基準タイミングにおける回転角を精度良く算出する回転角検出装置を提供する。【解決手段】回転角検出装置５０１のＡＤ変換器４１、４２は、複数の回転角センサ素子３１、３２、３３が検出対象の回転角に応じてアナログ出力したｃｏｓ信号及びｓｉｎ信号を取得し、デジタル値であるｃｏｓ値及びｓｉｎ値に一定の変換周期で逐次的に変換する。角度算出処理部５１は、いずれかの回転角センサ素子又はＡＤ変換器の故障時に代替可能な複数通りの角度を算出する。角度の算出は、基準タイミングを時間軸での中心としたとき前後対称となる一つ又は複数の変換タイミングで変換されたｃｏｓ値及びｓｉｎ値に基づいて行われる。また、算出に用いられるｃｏｓ値及びｓｉｎ値の相対的な変換タイミングが異なる。【選択図】図２