A nail guiding device of a nailer includes a guiding portion for guiding the nails along a straight path. The nailer has a reception recess with which a guiding member is pivotably connected. A guiding plate includes two grooves defined along two sides thereof. The strike plate and nails are slidably moved along the guiding plate between the two grooves. The guiding plate has first and second slots. The guiding member has a pivot pivotably inserted in the reception recess, a first guiding portion, a first rail, a second rail parallel to the first rail and a second guiding portion. The guiding member has a resilient arm connected thereto which contacts an inside of the body of the nailer. The first and second rails swing through the first and second slots so as to guide the nails to be ejected along a straight path.