A piezoelectric lighter incorporates with a safety arrangement which includes is movably mounted on a casing in a vertical movable manner wherein a guiding slot is provided on top of the casing to communicate with an exterior thereof. The control unit positions the movable element at a predetermined position by making the movable element abut the stopper. With respect to a cell of interest on the one-dimensional structured grid, a slope is set to zero if a forward difference and a backward difference of the function f have different signs, and to a value twice as large as a smaller one of absolute values of the forward difference and the backward difference if the forward difference and the backward difference have the same sign.