A sprinkler mounting device comprising: T-shaped frames mounted on a ceiling at a predetermined interval in parallel; a support bar mounted on the T-shaped frames at right angles from the T-shaped frames; comprising a mounting bracket, the mounting bracket including a U-shaped bracket body having a closed face bent between parallel upper and lower faces for allowing the support bar to be insertedly mounted between the upper and lower faces, mounting slots (111, 121) respectively formed on the upper and lower faces for insertedly fitting a reducer onto the upper and lower faces from the front, retaining jaw portions (112, 122), each being formed at one side of each of the mounting slots (111, 121), a lever mounted rotatably on a first hinge shaft at the other side of the mounting slots (111, 121), and a tightening member bent in correspondence to a section of the reducer, the tightening member having a locking recess formed at one side thereof and caught to the retaining jaw portions (112, 122) and a hinge space portion formed at the other side thereof, the tightening member being mounted rotatably on a second hinge shaft of the lever; and the reducer insertedly mounted into the mounting slots (111, 121) of the mounting bracket characterized in that the locking means comprises: elongated holes (113, 123) formed at sides of the upper and lower faces; a spring having a spirally wound portion, to which the first hinge shaft is fit, and vertical end portions extending from both ends of the spirally wound portion and being inserted into the elongated holes (113, 123); and a one-way latch portion formed at one end of the lever in such a way as to correspond to the vertical end portion. T-shaped frames mounted on a ceiling at a predetermined interval in parallel; a support bar mounted on the T-shaped frames at right angles from the T-shaped frames; comprising a mounting bracket, the mounting bracket including a U-shaped bracket body having a closed face bent between parallel upper and lower faces for allowing the support bar to be insertedly mounted between the upper and lower faces, mounting slots (111, 121) respectively formed on the upper and lower faces for insertedly fitting a reducer onto the upper and lower faces from the front, retaining jaw portions (112, 122), each being formed at one side of each of the mounting slots (111, 121), a lever mounted rotatably on a first hinge shaft at the other side of the mounting slots (111, 121), and a tightening member bent in correspondence to a section of the reducer, the tightening member having a locking recess formed at one side thereof and caught to the retaining jaw portions (112, 122) and a hinge space portion formed at the other side thereof, the tightening member being mounted rotatably on a second hinge shaft of the lever; and the reducer insertedly mounted into the mounting slots (111, 121) of the mounting bracket characterized in that the locking means comprises: elongated holes (113, 123) formed at sides of the upper and lower faces; a spring having a spirally wound portion, to which the first hinge shaft is fit, and vertical end portions extending from both ends of the spirally wound portion and being inserted into the elongated holes (113, 123); and a one-way latch portion formed at one end of the lever in such a way as to correspond to the vertical end portion.