This specification discloses an adjusting mechanism of an instrument pedal that is pivotally disposed on a pivotal axis of a base to sway along the radial direction of the pivotal axis. The adjusting mechanism has a foundation. There is an arc surface around the radial direction of the pivotal axis outside the foundation. A sliding groove is formed along the radial direction of the arc surface. A fixed hole is formed on the pivotal axis corresponding to the sliding groove. One end of the fixing element goes through the sliding groove and connects to the fixing hole. The other end of the fixing element engages with the arc surface on both sides of the sliding groove for fixing the adjusting mechanism.