The utility model provides a speed reducer, in particular to a compact type speed reducer with a straight tooth bevel gear. The compact type speed reducer with the straight tooth bevel gear comprises a box. A worm and a worm wheel are arranged in the box and are in meshed transmission. One end of the worm extends out of the box. The extending end of the worm is located to the box through an upper end cover. The left side end of the worm wheel is located to the box through an end cover. The right end of the worm wheel is located to the box through a channel. The right side end of the worm wheel is sleeved with the straight tooth bevel gear. A temperature sensor is arranged in the box. The compact type speed reducer with the straight tooth bevel gear is simple in structure, convenient to assemble, and high in adaptability, product performance is improved, and the service life is prolonged.