There are provided a relative angle detection device suitable for expanding a torque detection range, and a torque sensor, an electric power steering device and a vehicle including the relative angle detection device. Based on a first sine signal representing sin(θos+Δθ) and a first cosine signal representing cos(θos+Δθ) in accordance with a rotation angle(θis) of a first multipolar ring magnet that synchronously rotates with an input shaft from between the coaxially arranged input shaft and an output shaft, and based on a second sine signal representing sin θos and a second cosine signal representing cos θos in accordance with a rotation angle(θos) of a second multipolar ring magnet that synchronously rotates with the output shaft, sin Δθ and cos Δθ are calculated in accordance with a relative angle(Δθ) between the input shaft and the output shaft, and from Δθ=arctan(sin Δθ/cos Δθ), the relative angle(Δθ) is calculated.