A clutch pedal effort reduction structure using a detent may include: a pedal arm to rotate with respect to a hinge fixed to a vehicle body; and a spring module to reduce a pedal effort when the pedal arm rotates with respect to the hinge. In particular, the pedal arm includes a pedal arm groove provided with one or more curved portions having a curvature and rotates depending on a rotation of the pedal arm, and the spring module includes a support portion held in close contact with the pedal arm groove so as to be in contact with the one or more curved portions when the pedal arm rotates. And a force by which the spring module presses the pedal arm is changed according to a curvature of the curved portions which the support portion is in contact with when the pedal arm is operated.