A display device for a construction machine has a display switching means, output control means, operation detecting means, and display prohibiting means. The display switching means switches information displayed on a monitor placed in an operation cabin, where the switching is made to prevent display of unnecessary information on the monitor while the construction machine is performing work. The output control means selects display information recorded in information recording means and outputs the selected information to the monitor. The operation detecting means detects whether or not the construction machine is in a working state. When the operation detecting means detects that the construction machine is in the working state, display switching operation of the monitor is performed by the display switching means, and the display prohibiting means prohibits the display of specific information.