Friction drive device

A friction drive device comprising:

• a first roller acting as one of an input roller and an output roller directly contacted with the input roller and having a support part, the support part being apart from a contactable surface of said first roller in a rotating axis direction of said first roller;
• a second roller that acts as the other of the input roller and the output roller and receives press force from said first roller at a first contact point of said first and second rollers so as to transmit mechanical power between said first and second rollers;
• and
• a cam member located apart from the contactable surface in the rotating axis direction and supporting said first roller through the support part and having a cam formed with a cam slope on which the support part of said first roller is pressed by reaction torque from said second roller that is caused by transmission torque applied from said first roller, the cam slope being formed to have an angle with respect to a tangent line at the first contact point so that a center connecting line passing through a center of said first roller and a center of said second roller can move relative to the cam in a circumferential direction of said second roller to depart from the center connecting line located when the transmission torque is zero and a second contact point of the support part of said first roller and the cam slope can approach the center of said second roller as the transmission torque increases.