A pedal exerciser includes a shaft rotatably mounted to a shaft coupling portion of a base. Two pedal rods are mounted on two ends of the shaft. A non-automatic mechanism is mounted to the base and releasably coupled to the shaft. An automatic mechanism is mounted to the base and releasably coupled to the shaft. The automatic mechanism includes a power source. A switching mechanism includes a driving wheel coupled to the shaft. The driving wheel is mounted around the shaft and located between the non-automatic mechanism and the automatic mechanism. The driving wheel is movable between the non-automatic mechanism and the automatic mechanism to control engagement/disengagement of the driving wheel with/from the non-automatic mechanism and the automatic mechanism, allowing switching between a non-automatic mode and an automatic mode.