To provide an engine room structure of a working machine capable of further reducing noise while improving the refrigeration efficiency of an engine or the like.

The engine room structure of the working machine is equipped with an engine room 4 formed by storing a heat exchanger 1, a cooling fan 2 and an engine 3. The engine room is divided into two box-shaped rooms 4a and 4b by making the heat exchanger 1 as a partition, air openings 8b, 8c, 8d and 30b; 8a, 10a and 30a connecting the inside and the outside of the engine room 4 are provided to the two divided rooms 4a and 4b, respectively, and sound absorption blades 15, 20, 24 and 35 formed by putting sound absorbing materials 17, 23, 26 and 37 on both sides or one side of plate materials 16, 22, 25 and 36 are provided to one room side 4a whereon the cooling fan 2 and the engine 3 are arranged between the two rooms 4a and 4b along a direction connecting the heat exchanger 1 to the air openings 8b, 8c, 8d and 30b of the one room side 4a.