An acceleration detector includes a base portion, a plate-like movable portion connected to the base portion via a joint portion, an acceleration detecting element laid over the base portion and the movable portion, and a supporting portion having a part extending along the movable portion from the base portion, as viewed in a plan view. A mass portion partly overlapping the supporting portion, as viewed in a plan view, is arranged on at least one of two main surfaces of the movable portion. The movable portion is displaceable about the joint portion as a fulcrum in a direction intersecting the main surface according to an acceleration applied in the direction intersecting the main surface. A space is provided between the mass portion and the supporting portion in an area where the mass portion and the supporting portion overlap each other.
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