Rotation angle detection device

A rotation angle detection device for detecting the absolute angle of a shaft rotating with respect to a non-rotating member over a plurality of revolutions, comprising:

• at least one target rotating in unison with the shaft;
• a rotating member mechanically engaged with the shaft for rotating at a different rotation speed from the shaft as the shaft rotates;
• a first sensor adjacent to a circular path of the of the target whose output signal changes when the target is approached;
• a second sensor adjacent to the rotating member that detects a rotation angle of the rotating member within one rotation;
• and
• a computing section that calculates the absolute angle of the shaft based on the output signal of the first sensor and the rotation angle of the rotating member detected by the second sensor,
• wherein the output signal of the first sensor changes at a period different from a rotation period of the rotating member when the shaft rotates, and
• wherein the computing section detects the absolute angle of the shaft at that time from the rotation angle of the rotating member when the output signal of the first sensor changes.