A beam-intensity-depletion (BID) method to determine the direction of the transition dipole moment in the molecular frame was demonstrated in the polarized laser photolysis of the oriented CH3I beam. The depletion of the primary beam intensity of oriented CH3I via the photodissociation with linearly polarized laser light was measured as a function of molecular orientation and the polarization angle of the polarized laser light. The (X-A) transition of CH3I in the 111] rotational state was probed with linearly polarized laser light at 248 nm. The orientational dependence of the BID indicates that this transition is predominantly (96 +/- 4%) a parallel-type transition at this wavelength. This result is in good agreement with the previous result deduced by the angular distribution of the photofragment, showing the usefulness of this direct method.