A mobile robot having wheels which maintain contact forces against a surface even when the mobile robot meets an obstacle on the surface and a body of the mobile robot is forced up against the obstacle. The mobile robot easily surmounts the obstacle on the surface, without requiring any sensors, any specific controller, any specific traveling unit to surmount over the obstacle, or any specific drive unit to drive the specific traveling unit. The mobile robot includes the body, the wheels connected with the body which move arcuately relative to the body, and a wheel guide unit coupled at a first end to the body and at a second end to a hub of each of the wheels. The wheel guide unit is contracted when the body is spaced apart from the surface on which the robot moves. However, the wheel guide unit expands to allow the wheel to be in contact with the surface when the body comes into contact with the surface.