To provide a suspension device to leave the center of gravity of a motorcycle body at the rear side by increasing the air reaction force of a front fork during brake when the motorcycle body on the front side of the motorcycle is sunk and further suppress movement of the center of gravity of the motorcycle body to the rear side by decreasing the air reaction force of a front fork during acceleration when the motorcycle body on the front side is floated, and improve running stability of the motorcycle.

An air cylinder device 15 consisting of a cylinder 16 and a rod 17 slid in the cylinder 16 is pivotally supported between a motorcycle body frame 1 and an oscillation arm 11 to rotatably support a rear wheel 12 such that an air chamber in the air cylinder device 15 is compressed during braking and the air chamber is expanded during acceleration. The air chamber in the air cylinder device 15 is connected to an air chamber in a front fork 4 through a conduit 18.