To provide an inner stair case type double deck bus which is excellent in comfortability and economical efficiency by lessening a sense of oppression due to the ceilings of a second floor cabin and a first floor service cabin to passengers, letting a driver and passengers get on/off a driver's seat and the second floor cabin only through an entrance at the front end part, and letting the paired right and left longitudinal members of a chassis frame be mounted through the frame.

This bus is provided with a first inner stair case 1 which is mounted on a second floor 3 at the front center line of a car body from a first floor 2 at one side in the front end part of the car body while being bent in a right angle shape in the longitudinal direction from the right and left directions, and a second inner stair case 4 which is mounted in the longitudinal direction in a space between the right and left longitudinal members 6 of a chassis frame 5, and is connected to a first floor longitudinal passage 14 floor provided at the level of a lower end part of each longitudinal member 6 at the center part of the car body and the second floor 3, and with a first side part floor 15 provided at the level higher than that of the first floor longitudinal passage 14 floor.