A light-projecting device for performing a scan of a light in a tracing period wherein an image is displayed and in a retracing period wherein an image is not displayed, the device comprising: a light source (11a, 11b, 11c) adapted to emit a light; a first light-receiving Integrated Circuit, or light-receiving IC (26a, 26b), adapted to detect a light quantity of the light emitted from the light source; a controller adapted to control the light source based on a detection result of the first light-receiving IC and to control the driving signals of a scanner; wherein the scanner comprises a mirror and is adapted to: perform a first scan of the light in a first direction and a second direction opposed to the first direction, the first scan in the first direction being performed in the tracing period, and the first scan in the second direction being performed in the retracing period, and while performing the first scan, to perform a second scan of the light in a direction orthogonal to the first direction, wherein, in the tracing period, the scanner is adapted to perform the second scan with the mirror swinging in a first angle range (θh1), wherein, in the retracing period, the scanner is adapted to perform the second scan with the mirror swinging in a second angle range (θh2) that is greater than the first angle range (θh1), wherein, in the retracing period, the controller is adapted to cause the light source to emit the light when the scanner performs the second scan at a swinging angle which is inside the second angle range (θh2) and outside the first angle range (θh1), and the controller is adapted to cause the light source not to emit the light when the scanner performs the second scan at a swinging angle which is inside the first angle range (θh1), the light-projecting device further comprising a light-blocking frame adapted to block the light projected outside a region in which the second scan is performed in the first angle range (θh1), and wherein the first light-receiving IC (26a, 26b) is adapted to detect the light quantity in the retracing period, when the second scan is performed at a swinging angle which is inside the second angle range (θh2) and outside the first angle range (θh1). a light source (11a, 11b, 11c) adapted to emit a light; a first light-receiving Integrated Circuit, or light-receiving IC (26a, 26b), adapted to detect a light quantity of the light emitted from the light source; a controller adapted to control the light source based on a detection result of the first light-receiving IC and to control the driving signals of a scanner; wherein the scanner comprises a mirror and is adapted to: perform a first scan of the light in a first direction and a second direction opposed to the first direction, the first scan in the first direction being performed in the tracing period, and the first scan in the second direction being performed in the retracing period, and while performing the first scan, to perform a second scan of the light in a direction orthogonal to the first direction, perform a first scan of the light in a first direction and a second direction opposed to the first direction, the first scan in the first direction being performed in the tracing period, and the first scan in the second direction being performed in the retracing period, and while performing the first scan, to perform a second scan of the light in a direction orthogonal to the first direction, wherein, in the tracing period, the scanner is adapted to perform the second scan with the mirror swinging in a first angle range (θh1), wherein, in the retracing period, the scanner is adapted to perform the second scan with the mirror swinging in a second angle range (θh2) that is greater than the first angle range (θh1), wherein, in the retracing period, the controller is adapted to cause the light source to emit the light when the scanner performs the second scan at a swinging angle which is inside the second angle range (θh2) and outside the first angle range (θh1), and the controller is adapted to cause the light source not to emit the light when the scanner performs the second scan at a swinging angle which is inside the first angle range (θh1), the light-projecting device further comprising a light-blocking frame adapted to block the light projected outside a region in which the second scan is performed in the first angle range (θh1), and wherein the first light-receiving IC (26a, 26b) is adapted to detect the light quantity in the retracing period, when the second scan is performed at a swinging angle which is inside the second angle range (θh2) and outside the first angle range (θh1).