For non-invasive functional localization of language-related area in the inferior frontal gyrus (IFG), we propose a modified method of speech arrest (SA) induced by transcranial magnetic stimulation (TMS) using real-time optical navigation. Instead of usual overlearned speech production such as counting numbers or reciting the days of the week, we used reading of an unfamiliar manuscript of Aesop's Fable for a speech task. While participants were reading aloud the manuscript, TMS pulse sequences of 5Hz for 2 seconds were given at pseud-random timing. Stimulation site was monitored through a real-time navigation system in which the participant's head position was superimposed on his/her pre-obtained structural MRI image. First, the upper end of the ascending ramus of lateral sulcus on the left hemisphere was identified and then stimulation procedure was repeated by moving positions of the coil on a grid of approximately 1 by 1 cm in order to find a site eliciting maximum speech distortion (SA hot-spot). Once SA hot-spot at left hemisphere was identified, we next applied the stimulation to the homologous position on the right hemisphere. As a result, we confirmed that SA hot-spot can be identified at the left IFG (Broca's area) in 24 out of 28 subjects. In 5 subjects, right IFG stimulation also induced speech distortion. It was noteworthy that we successfully induced SA with lower TMS intensity (88% of active motor threshold) than those of previous reports. The difference of intensity may result from the selection of the task. This low intensity stimulation made possible to reduce not only the discomfort of the participants but also the contaminative stimulation of the facial muscles and adjacent motor cortices governing the oral and jaw muscles. SA with low intensity TMS can be a promising non-invasive technique for clinical tests as well as cognitive neurophysiological studies.