An impact detector includes a first determination unit operable to determine whether or not an absolute value of an acceleration in a direction of Y axis exceeds 1G, and an impact determination unit operable to output a predetermined impact detection signal which indicates detection of impact in a direction of Z axis in response to an absolute value of an acceleration in a direction of X axis exceeding 1G within a predetermined time period T after the first determination unit determines that the absolute value of the acceleration in the direction of Y axis exceeds 1G.