To provide an economical biaxial acceleration sensor with comparatively simple component constitution.

In a hollow case 12, a movable body 14 moveable in X and Y directions under the application of the acceleration is disposed. A support members 16 support the moveable body 14 to the X direction and the Y direction to the case 12. A light emitting device 18 fixed in the movable body 14 emits a light beam OB vertically down ward. On the bottom of the case 12 a two-dimensional photoreceptor 22 is fixed. A light convergence element 20 disposed in the movable body 14 make the light beam OB emitted from the light emitting device 18 condense onto a two-dimensional photoreceptor 22 as the condensing beam OB.