Master cylinder device for rear wheel brake of motorcycle and arrangement method of master cylinder device for rear wheel brake of motorcycle

A master cylinder device for a rear wheel brake of a motorcycle comprising:

• a master cylinder that discharges brake fluid when a piston thereof is pushed by depression of a brake pedal;
• and
• a reserve tank integrally formed with a cylinder body of the master cylinder,
• wherein a contour of a rear wheel side of the master cylinder device extending continuously from a bottom end of the master cylinder body in a vertical direction to an upper end of the reserve tank in the vertical direction is linearly formed to be oriented obliquely rearward and upward in a vehicle side view, wherein a linear shape of the contour of the rear wheel side of the master cylinder device is formed by a plate-shaped rib protruding from the cylinder body toward the rear wheel side;
• and the rib is provided along an inner edge of a bottom surface of the reserve tank in a vehicle width direction.