A rotation angle detection device comprising: a first sensor that is supplied with power when a power switch is on and outputs a first sensor signal in accordance with a rotation of a motor rotation shaft of a motor, and to which power supply is stopped when the power switch is off; an angular position calculation unit that is supplied with power when the power switch is on and calculates angular position information representing an angular position of the motor rotation shaft based on the first sensor signal, and to which power supply is stopped when the power switch is off; a second sensor that outputs a second sensor signal including a sine-wave signal and a cosine-wave signal in accordance with a rotation of the motor rotation shaft; a power management unit that supplies first power that is continuous power to the second sensor when the power switch is on, supplies second power that is intermittent power having a voltage lower than the first power to the second sensor when the power switch is off, and outputs rotation number information representing a rotation number of the motor rotation shaft based on the second sensor signal; and a rotation angle calculation unit that is supplied with power when the power switch is on and calculates rotation angle information representing a rotation angle of the motor rotation shaft based on the angular position information and the rotation number information, and to which power supply is stopped when the power switch is off, wherein the power management unit includes: a power supply unit that generates the first power and the second power; characterized by a comparator (58a, 58b) that operates using the first power supplied from the power supply unit as a power source and compares a first reference voltage based on a voltage of the first power and the second sensor signal when the power switch is on, and operates using the second power supplied from the power supply unit as a power source and compares a second reference voltage based on a voltage of the second power and the second sensor signal when the power switch is off; and a counter (58c, 58d) that detects a rotation number of the motor rotation shaft by counting an output of the comparator (58a, 58b). a first sensor that is supplied with power when a power switch is on and outputs a first sensor signal in accordance with a rotation of a motor rotation shaft of a motor, and to which power supply is stopped when the power switch is off; an angular position calculation unit that is supplied with power when the power switch is on and calculates angular position information representing an angular position of the motor rotation shaft based on the first sensor signal, and to which power supply is stopped when the power switch is off; a second sensor that outputs a second sensor signal including a sine-wave signal and a cosine-wave signal in accordance with a rotation of the motor rotation shaft; a power management unit that supplies first power that is continuous power to the second sensor when the power switch is on, supplies second power that is intermittent power having a voltage lower than the first power to the second sensor when the power switch is off, and outputs rotation number information representing a rotation number of the motor rotation shaft based on the second sensor signal; and a rotation angle calculation unit that is supplied with power when the power switch is on and calculates rotation angle information representing a rotation angle of the motor rotation shaft based on the angular position information and the rotation number information, and to which power supply is stopped when the power switch is off, wherein the power management unit includes: a power supply unit that generates the first power and the second power; characterized by a comparator (58a, 58b) that operates using the first power supplied from the power supply unit as a power source and compares a first reference voltage based on a voltage of the first power and the second sensor signal when the power switch is on, and operates using the second power supplied from the power supply unit as a power source and compares a second reference voltage based on a voltage of the second power and the second sensor signal when the power switch is off; and a counter (58c, 58d) that detects a rotation number of the motor rotation shaft by counting an output of the comparator (58a, 58b). a power supply unit that generates the first power and the second power; characterized by a comparator (58a, 58b) that operates using the first power supplied from the power supply unit as a power source and compares a first reference voltage based on a voltage of the first power and the second sensor signal when the power switch is on, and operates using the second power supplied from the power supply unit as a power source and compares a second reference voltage based on a voltage of the second power and the second sensor signal when the power switch is off; and a counter (58c, 58d) that detects a rotation number of the motor rotation shaft by counting an output of the comparator (58a, 58b).