An angle detection device, comprising: an angle sensor configured to output a first sine wave signal and a second sine wave signal having phases that are different from each other by 90 degrees in accordance with rotation of a detection target; an angle calculator configured to calculate an angle signal corresponding to a rotation angle of the detection target based on the first sine wave signal and the second sine wave signal; and an angle sensor abnormality determiner (4a-4e) configured to determine an abnormality of the angle sensor based on the first sine wave signal and the second sine wave signal, the angle sensor abnormality determiner (4a-4e) including: an amplitude signal calculator configured to calculate an amplitude signal based on a square root of a sum of squares, which is a value obtained by squaring and then adding the first sine wave signal and the second sine wave signal; a first angle signal calculation processor (6, 8) configured to calculate a first angle signal based on the first sine wave signal and the amplitude signal; a second angle signal calculation processor (7, 9) configured to calculate a second angle signal based on the second sine wave signal and the amplitude signal; and an abnormality determination processor (13, 413, 513, 14, 14b) configured to determine the abnormality of the angle sensor based on an angle error between the first angle signal and the second angle signal; wherein the amplitude signal calculator is configured to set, as the amplitude signal, a value obtained by causing the square root of the sum of the squares to pass through a high cut filter having a cutoff frequency set in advance; wherein the set cutoff frequency is higher than a variable frequency of an amplitude value of the first sine wave signal or the second sine wave signal due to heat generation and wherein the abnormality determination processor (13, 413, 513, 14, 14b) is configured to determine that the angle sensor is abnormal when a difference between the filtered amplitude signal and the square root of the sum of the squares is equal to or larger than a setting value set in advance. an angle sensor configured to output a first sine wave signal and a second sine wave signal having phases that are different from each other by 90 degrees in accordance with rotation of a detection target; an angle calculator configured to calculate an angle signal corresponding to a rotation angle of the detection target based on the first sine wave signal and the second sine wave signal; and an angle sensor abnormality determiner (4a-4e) configured to determine an abnormality of the angle sensor based on the first sine wave signal and the second sine wave signal, the angle sensor abnormality determiner (4a-4e) including: an amplitude signal calculator configured to calculate an amplitude signal based on a square root of a sum of squares, which is a value obtained by squaring and then adding the first sine wave signal and the second sine wave signal; a first angle signal calculation processor (6, 8) configured to calculate a first angle signal based on the first sine wave signal and the amplitude signal; a second angle signal calculation processor (7, 9) configured to calculate a second angle signal based on the second sine wave signal and the amplitude signal; and an abnormality determination processor (13, 413, 513, 14, 14b) configured to determine the abnormality of the angle sensor based on an angle error between the first angle signal and the second angle signal; wherein the amplitude signal calculator is configured to set, as the amplitude signal, a value obtained by causing the square root of the sum of the squares to pass through a high cut filter having a cutoff frequency set in advance; wherein the set cutoff frequency is higher than a variable frequency of an amplitude value of the first sine wave signal or the second sine wave signal due to heat generation and wherein the abnormality determination processor (13, 413, 513, 14, 14b) is configured to determine that the angle sensor is abnormal when a difference between the filtered amplitude signal and the square root of the sum of the squares is equal to or larger than a setting value set in advance. an amplitude signal calculator configured to calculate an amplitude signal based on a square root of a sum of squares, which is a value obtained by squaring and then adding the first sine wave signal and the second sine wave signal; a first angle signal calculation processor (6, 8) configured to calculate a first angle signal based on the first sine wave signal and the amplitude signal; a second angle signal calculation processor (7, 9) configured to calculate a second angle signal based on the second sine wave signal and the amplitude signal; and an abnormality determination processor (13, 413, 513, 14, 14b) configured to determine the abnormality of the angle sensor based on an angle error between the first angle signal and the second angle signal; wherein the amplitude signal calculator is configured to set, as the amplitude signal, a value obtained by causing the square root of the sum of the squares to pass through a high cut filter having a cutoff frequency set in advance; wherein the set cutoff frequency is higher than a variable frequency of an amplitude value of the first sine wave signal or the second sine wave signal due to heat generation and wherein the abnormality determination processor (13, 413, 513, 14, 14b) is configured to determine that the angle sensor is abnormal when a difference between the filtered amplitude signal and the square root of the sum of the squares is equal to or larger than a setting value set in advance.