An angular acceleration sensor includes a planar surface extending along an X-Y plane, a fixed portion, a weight, a beam, and piezoresistors. The weight is supported by the fixed portion. The beam extends along an Y-axis and is connected to the fixed portion and the weight. The beam includes through-holes extending therethrough in a Z-axis direction and protrusions protruding in an X-axis direction. The positions of the piezoresistors in the Y-axis direction overlap those of the through-holes and are displaced from those of the width-direction protrusions.