a shock sensor is able to detect an externally applied acceleration . a weight is fixed to a first end of a first supporting member . the weight is rotatably movable about an opposite end of the supporting member . a second supporting member , having an indicating portion , is provided under the first supporting member . a spring member is integrally formed with the second supporting member so as to hold the second supporting member either at an upper position to support the weight or at a lower position where a predetermined acceleration is detected . whether or not the shock sensor has detected that an acceleration exceeding the predetermined value has been applied to the sensor is indicated by the position of the indicating portion .