An acceleration sensor which is inexpensive and accomplishes its small-size and light-weight structure, and a manufacturing method thereof. A sensor unit provided on a base is sealed by a cap joined to a frame portion of the base in an eutectic manner. The cap includes a cap main body made of a semiconductor material having a conductive property and a metal film provided on the circumferential edge of the cap main body. The frame portion includes a frame main body made of doped polysilicon, a diffusion preventive film selectively provided on the frame main body, and a joining layer. The joining layer has one area as a conductive portion made of a conductive material, and another area as a joining portion made of a semiconductor.