An accelerometer includes a main body, a displacing member, a scale, and a detecting unit. The displacing member is attached to the main body and has a displacing portion displaced relative to the main body at least in a direction of acceleration measurement in accordance with a force applied. The scale is provided to one of the main body and the displacing portion to detect displacement in the direction of acceleration measurement. The detecting unit is provided to the other one of the main body and the displacing portion to optically read the relative displacement of the scale. The acceleration applied to the main body is detected by the reading of the relative displacement of the scale performed by the detecting unit during relative displacing of the displacing portion.