The invention is intended to provide a technique regarding sensor nodes for impact detection to enable the intensities of impacts to be determined in a multi-value or analog mode and to reduce the power consumption of sensor nodes. The sensor node is provided with a shock detection sensor comprising a piezoelectric element unit which generates an electric charge corresponding to an external impact, a capacitor which rectifies and accumulates the electric charge so generated, and a voltage detector which operates on the accumulated power and externally outputs a signal when the accumulated voltage reaches a preset level; a stand-by control object section which is caused by the external signal to return from a stand-by state and to operate; and a power supply which feeds power to the stand-by control object section, wherein the operation of the stand-by control object section is triggered by the signal of impact detected by the piezoelectric element unit.