A vehicular driving speed detecting device which comprises a stator having R reed switches connected in parallel, wherein R represents an integer of two or more, at the interval of a central angle of (2 pi /n)(1 + KR) radians wherein K represents zero or a natural number of (n/R - 1) or less, and a rotor rotatably inserted in said stator and having n/R magnets near the periphery thereof at the interval of a central angle of (2 pi R)/n, one of said magnets being adapted to keep, by an angle of rotation gamma defined by the formula 0