A sensing apparatus is disclosed. The sensing apparatus comprises a first image capturing module, a second image capturing module, a calculating module, and a controlling module. The first image capturing module and the second image capturing module capture a first image and a second image related to a plurality of objects respectively at a specific time. The calculating module obtains a 3-D position of an object according to the first image and the second image and obtains a 3-D displacement of the object according to the 3-D position and a former 3-D position of the object. If any one of 3-D displacements corresponding to the objects is approximately vertical, the controlling module controls an electrical apparatus to perform a first function. If a weighting average of approximately horizontal vector components of all 3-D displacements meets a condition, the controlling module controls the electrical apparatus to perform a second function.