An air circuit breaker having a mechanical trip indicating mechanism, in an air circuit breaker including a switching mechanism, an actuator having an output link for providing a mechanical driving force, a first link unit connected between the output link of the actuator and the switching mechanism for applying the mechanical driving force from the output link to the switching mechanism to perform a trip operation, a front surface plate provided with a manipulating unit accessible by a user, the air circuit breaker comprising: a first rotation lever connected to the first link unit, a second link unit limitedly moved by the first rotation lever, a bias spring for applying an elastic biasing force to the second link unit to be moved in one direction, a second rotation lever installed to be rotatable with coming in contact with one end portion of the second link unit, and a mechanical trip indicating mechanism supported by the front surface plate and having an indicating portion exposed to the front surface plate to indicate the tripped state of the air circuit breaker and a driving force receiving portion contacted with the second rotation lever to receive a driving force from the second rotation lever to expose the indicating portion.