Abstract: The durability and detection accuracy of a sensor unit may possibly decrease due to radiation heat generated from work pieces while they are welded together. A sensor device includes a sensor unit, a housing case, and a shielding member. The sensor unit is a device for measuring the shapes of the work pieces W or the distance to the work pieces W. The housing case houses the sensor unit and has formed therein a pass-through portion for laser beam projection and a pass-through portion for detection that pass a laser beam L1 from a laser beam projection unit and a laser beam L2 directed to a detection unit, respectively. The shielding member is attached to the housing case, and shields radiation heat directed toward the lower surface of the housing case among radiation heat generated while the work pieces W are welded together. The shielding member is made of a material with lower thermal conductivity than that of the housing case.