An impact sensor comprises a silicon substrate; an insulating layer formed over the silicon substrate; a plurality of beams having flexibility that are formed of conductive silicon material; a fixing portion to fix a fixed end of each of the beams, the fixing portion being formed of conductive silicon material; a fixed end line at whose one end is formed the fixing portion, the fixed end line being formed of conductive silicon material on the insulating layer; and a free end line having a pressing portion that faces a free end of each of the beams via a space, the free end line being formed of conductive silicon material on the insulating layer. Respective beam widths, each measured in a direction orthogonal to a length direction joining the fixed end and the free end, of the plurality of beams are set different from each other, thus reducing the space occupied by the sensor.