A working machine comprising: a lower traveling body; and an upper slewing body provided on the lower traveling body so as to be able to slew and the upper slewing body being configured to perform a working operation according to an operation of an operator, wherein the upper slewing body includes: an engine provided in a rear portion of the upper slewing body; an exhaust pipe (11a to 11c) extending from the engine in order to guide exhaust gas; a rear wall portion covering an engine room accommodating the engine from a rear side; a floor wall portion disposed so as to cover the engine room from a lower side and the floor wall portion having an exhaust opening that opens the engine room to a lower side; and a pair of vertical plates (21, 23) standing upright on both left and right sides of the exhaust opening of the floor wall portion and the pair of vertical plates (21, 23) extending in a front-rear direction on a lower side of the engine, one of the pair of vertical plates is a pipe-insertion vertical plate, and the pipe-insertion vertical plate includes a rear end portion having a proximate rear end surface disposed adjacent to the rear wall portion so as to prevent the exhaust pipe (11a to 11c) from passing between the pipe-insertion vertical plate and the rear wall portion, characterized in that the pipe insertion vertical plate includes a cutout portion formed by recessing a rear end surface of the pipe-insertion vertical plate toward a front side with respect to the proximate rear end surface, the exhaust pipe is disposed across an outer position of the pair of vertical plates (21, 23) and an inner position of the pair of vertical plates (21, 23) through the cutout portion and has a distal end portion for discharging the exhaust gas, and the distal end portion of the exhaust pipe (11a to 11c) is disposed at the inner position of the pair of vertical plates (21, 23), and the distal end portion of the exhaust pipe (11a to 11c) extends along the exhaust opening in a state of facing the exhaust opening. a lower traveling body; and an upper slewing body provided on the lower traveling body so as to be able to slew and the upper slewing body being configured to perform a working operation according to an operation of an operator, wherein the upper slewing body includes: an engine provided in a rear portion of the upper slewing body; an exhaust pipe (11a to 11c) extending from the engine in order to guide exhaust gas; a rear wall portion covering an engine room accommodating the engine from a rear side; a floor wall portion disposed so as to cover the engine room from a lower side and the floor wall portion having an exhaust opening that opens the engine room to a lower side; and a pair of vertical plates (21, 23) standing upright on both left and right sides of the exhaust opening of the floor wall portion and the pair of vertical plates (21, 23) extending in a front-rear direction on a lower side of the engine, an engine provided in a rear portion of the upper slewing body; an exhaust pipe (11a to 11c) extending from the engine in order to guide exhaust gas; a rear wall portion covering an engine room accommodating the engine from a rear side; a floor wall portion disposed so as to cover the engine room from a lower side and the floor wall portion having an exhaust opening that opens the engine room to a lower side; and a pair of vertical plates (21, 23) standing upright on both left and right sides of the exhaust opening of the floor wall portion and the pair of vertical plates (21, 23) extending in a front-rear direction on a lower side of the engine, one of the pair of vertical plates is a pipe-insertion vertical plate, and the pipe-insertion vertical plate includes a rear end portion having a proximate rear end surface disposed adjacent to the rear wall portion so as to prevent the exhaust pipe (11a to 11c) from passing between the pipe-insertion vertical plate and the rear wall portion, characterized in that the pipe insertion vertical plate includes a cutout portion formed by recessing a rear end surface of the pipe-insertion vertical plate toward a front side with respect to the proximate rear end surface, the exhaust pipe is disposed across an outer position of the pair of vertical plates (21, 23) and an inner position of the pair of vertical plates (21, 23) through the cutout portion and has a distal end portion for discharging the exhaust gas, and the distal end portion of the exhaust pipe (11a to 11c) is disposed at the inner position of the pair of vertical plates (21, 23), and the distal end portion of the exhaust pipe (11a to 11c) extends along the exhaust opening in a state of facing the exhaust opening.