A substrate is fixed to a housing. Heating elements are mounted on a surface of the substrate on the housing-side. A radiating component is provided between the heating elements and the housing. A surface of the housing on the substrate-side includes accommodating recesses, a partitioning wall part, a peripheral wall part, and buffer parts. In each of the accommodating recesses, a corresponding one of the heating elements is accommodated. The partitioning wall part separates the heating elements from each other. The peripheral wall part surrounds the accommodating recesses and the partitioning wall part. Each of the buffer parts is formed between a corresponding one of the accommodating recesses and the peripheral wall part. Each of the buffer parts is formed to be higher than a bottom part of a corresponding one of the accommodating recesses, and to be lower than the peripheral wall part.