Lock-up device of torque converter

A lock-up device of a torque converter, comprising:

• an input side clutch supporter fixed to a front cover for transmitting power from a drive side;
• a plurality of clutch plates supported by the input side clutch supporter;
• a lock-up piston to pressurize the clutch plates to make a clutch connected;
• a piston guide supporting an end portion of the lock-up piston;
• a spring pack fixed to the lock-up piston, installed between the lock-up piston and the input side clutch supporter, the spring pack including:
• a first retainer plate installed on a side of the lock-up piston and fixed with the lock-up piston,
• a second retainer plate installed on a side of the input side clutch supporter, and
• an elastic body between the first retainer plate and the second retainer plate that presses the lock-up piston in a direction of releasing the clutch;
• and
• a relative rotation prevention mechanism that prevents relative rotation between the lock-up piston and the input side clutch supporter, the relative rotation prevention mechanism including:
• an outer gear on an exterior circumference of the first retainer plate of the spring pack, and
• an inner gear on an inner circumference of the input side clutch supporter and engaged with the outer gear.