A ranging device includes a light emission device configured to emit a light pulse sequence, a light guide device, a first light reception device configured to monitor an output optical power of the light emission device, and a second light reception device configured to receive a light pulse signal reflected by an object and determine a distance between the object and the ranging device based on the light pulse signal. The light guide device includes a light incident surface, a reflection surface, and a light emission surface. The reflection surface includes a first reflection surface and a second reflection surface. At least one of the first reflection surface or the second reflection surface has a curved surface shape. The light guide device is configured to receive part of radiation power emitted by the light emission device and conduct the part of the radiation power to the first light reception device.