There are provided a radiation-irradiation device and a monitor image display method for the radiation-irradiation device that allow a device operator to confirm a situation on the front side in a traveling direction in a case in which the device operator makes a radiation-irradiation device holding a radiation source travel and also allow the operator to confirm a situation around a subject in a case in which the device operator takes a radiation image. A radiation-irradiation device includes: direction detecting means (44) for detecting the direction of a radiation source； and display control means (22) for displaying an irradiation-direction image on a monitor (23) in a case in which the radiation source detected by the direction detecting means (44) is set to a direction other than a downward direction, displaying the irradiation-direction image on the monitor (23) in a case in which the radiation source is set to the downward direction and a first condition is satisfied, and displaying a front image on the monitor (23) in a case in which the radiation source is set to the downward direction and a second condition different from the first condition is satisfied.
