A cooling air introduction path is formed in a base of a sound proof case of an engine-driven work machine. The base is divided into upper and lower portions, and a space in the upper portion is divided by a separation wall and arranged below an air discharging chamber. The upper part of one space is covered with a arranging plate, a partition wall is erected on the arranging plate, and a cooling air introduction port is provided between the partition wall and the separation wall to provide an engine chamber and one space are communicated, a hole is provided in the plate below the chamber, and one space and the space in the lower portion are communicated and located below the chamber. A cooling air intake port is provided on lateral walls of the lower portion to communicate the space inside the lower portion with the outside of the machine.