A scanning mirror includes a mirror unit configured to reflect a laser beam, a supporter configured to cause the mirror unit to rotate and oscillate, and an oscillation sensor configured to output a monitor signal indicating oscillation of the mirror unit. A photodetector detects an intensity of the laser beam. When a value of the monitor signal falls out of a predetermined range of a normal operation and a value of the intensity detected by the photodetector fails to decrease, a breaking signal for causing the supporter to oscillate more than a breaking limit angle of the supporter is input. This scanning mirror and an image projection device using this scanning mirror can display an image at sufficient brightness safely.