A construction machine comprising: an automotive lower traveling structure; an upper revolving structure mounted on said lower traveling structure to be capable of revolving thereon; and a working mechanism provided to said upper revolving structure to be capable of lifting and tilting thereto, wherein said upper revolving structure comprises: a revolving frame forming a support structure; a floor member which is provided on said revolving frame and on which an operator's seat is mounted; a cab box which is provided to cover the periphery and the upper side of said floor member, forms an occupying space therein, and includes a door capable of opening/closing on an outer surface in one of the right-left direction; and an indoor unit in an air-conditioning unit mounted to said floor member for supplying intake air to said occupying space as conditioned air, characterized in that: said floor member comprises: a lever-pedal mounting part which is positioned in a front side and to which a traveling lever-pedal is mounted; an operator's seat mounting part which is positioned in a rear side to be surrounded by left and right side plates (11A, 11B) and a rear plate, and on which a risen-up platform is formed and said operator's seat is mounted; an indoor unit mounting surface part which is positioned in an indoor unit accommodating space under said platform of said operator's seat mounting part and on which said indoor unit is mounted; an entrance surface part which is positioned between said indoor unit mounting surface part and said lever-pedal mounting part and is provided in a side of said door in said cab box and on which an operator places a foot at getting-in/off; and a foot rest part which is provided to be surrounded by said lever-pedal mounting part, said indoor unit mounting surface part and said entrance surface part, and on which the operator seated on said operator's seat places a foot, wherein said lever-pedal mounting part and said foot rest part form a successive plane successively extending with each other in a height position where the operator seated on said operator's seat can place a foot, and said indoor unit mounting surface part and said entrance surface part form a successive plane successively extending with each other in a position lower by one step than a height position of said lever-pedal mounting part and said foot rest part. an automotive lower traveling structure; an upper revolving structure mounted on said lower traveling structure to be capable of revolving thereon; and a working mechanism provided to said upper revolving structure to be capable of lifting and tilting thereto, wherein a revolving frame forming a support structure; a floor member which is provided on said revolving frame and on which an operator's seat is mounted; a cab box which is provided to cover the periphery and the upper side of said floor member, forms an occupying space therein, and includes a door capable of opening/closing on an outer surface in one of the right-left direction; and an indoor unit in an air-conditioning unit mounted to said floor member for supplying intake air to said occupying space as conditioned air, characterized in that: a lever-pedal mounting part which is positioned in a front side and to which a traveling lever-pedal is mounted; an operator's seat mounting part which is positioned in a rear side to be surrounded by left and right side plates (11A, 11B) and a rear plate, and on which a risen-up platform is formed and said operator's seat is mounted; an indoor unit mounting surface part which is positioned in an indoor unit accommodating space under said platform of said operator's seat mounting part and on which said indoor unit is mounted; an entrance surface part which is positioned between said indoor unit mounting surface part and said lever-pedal mounting part and is provided in a side of said door in said cab box and on which an operator places a foot at getting-in/off; and a foot rest part which is provided to be surrounded by said lever-pedal mounting part, said indoor unit mounting surface part and said entrance surface part, and on which the operator seated on said operator's seat places a foot, wherein