A 3-dimensional measuring device includes: a light source unit; a projection optical system; a scanning mirror that is provided to be rotatable about a rotating shaft in a state of being inclined with respect to a shaft center of the rotating shaft to radiate a range-finding light within a plane crossing the rotating shaft in a rotary manner; a light-receiving optical system that receives a reflection range-finding light; a reference light optical system that is provided in a range outside a measuring range within a radiation range to receive and reflect the range-finding light as an internal reference light, the reference light optical system being capable of changing a light quantity of the internal reference light; and a light receiving element that receives the reflection range-finding light and the internal reference light.