A construction machine comprising: a lower travelling body; an upper slewing body turnable with respect to the lower travelling body; a control section to control travelling of the lower travelling body, and turning of the upper slewing body with respect to the lower travelling body; a turn angle detection section to detect a turn angle (α) of the upper slewing body with respect to the lower travelling body to input the detected turn angle (α) to the control section; an obstacle detection section attached to the upper slewing body to detect an obstacle and input a detection result to the control section, characterized in that the construction machine further comprises a storage section which stores, in advance, a plurality of monitoring region data pieces according to respective turn angles (α) of the upper slewing body with respect to the lower travelling body to determine the monitoring region, wherein the control section determines a monitoring region in which an obstacle is to be monitored, the monitoring region not including the lower travelling body, wherein the control section changes the monitoring region so as to not include the lower travelling body in the monitoring region, based on the turn angle (α) detected by the turn angle detection section, wherein the control section limits operation of at least one of travelling of the lower travelling body and turning of the upper slewing body when the obstacle detection section detects an obstacle being present in the monitoring region, wherein the control section selects a monitoring region data piece corresponding to the turn angle (α) detected by the turn angle detection section from the plurality of monitoring region data pieces stored in the storage section to determine the monitoring region, and wherein the storage section stores in advance the plurality of monitoring region data pieces according to a specification of the lower travelling body. a lower travelling body; an upper slewing body turnable with respect to the lower travelling body; a control section to control travelling of the lower travelling body, and turning of the upper slewing body with respect to the lower travelling body; a turn angle detection section to detect a turn angle (α) of the upper slewing body with respect to the lower travelling body to input the detected turn angle (α) to the control section; an obstacle detection section attached to the upper slewing body to detect an obstacle and input a detection result to the control section, characterized in that the construction machine further comprises a storage section which stores, in advance, a plurality of monitoring region data pieces according to respective turn angles (α) of the upper slewing body with respect to the lower travelling body to determine the monitoring region, wherein the control section determines a monitoring region in which an obstacle is to be monitored, the monitoring region not including the lower travelling body, wherein the control section changes the monitoring region so as to not include the lower travelling body in the monitoring region, based on the turn angle (α) detected by the turn angle detection section, wherein the control section limits operation of at least one of travelling of the lower travelling body and turning of the upper slewing body when the obstacle detection section detects an obstacle being present in the monitoring region, wherein the control section selects a monitoring region data piece corresponding to the turn angle (α) detected by the turn angle detection section from the plurality of monitoring region data pieces stored in the storage section to determine the monitoring region, and wherein the storage section stores in advance the plurality of monitoring region data pieces according to a specification of the lower travelling body.