there is provided a speed monitoring device which can use a low resolution position sensor and provide a high speed response without false detection . the speed monitoring device stores , in a memory unit , a permitted margin pm , a comparison distance vc which is a maximum movement distance permitted for a moving element within one cycle period , and positional data p of the moving element obtained from the present time t to m cycles ago . during speed determination , whether | p − p |& gt ; vc * n + pm holds true is determined for every integer n from 1 to m . when the inequality holds true , it is determined that the speed exceeds the speed limit .