The telescope method was used with solid-state detectors for measuring angular and energy distributions of complex particles emitted in nuclear reactions induced by 157-MeV protons on heavy nuclei (Ag, Au, Bi, Th). Both an isotropic and a forward-peaked emission of 4He, tritons, and deuterons were observed. Yields of 3He were found to be very low at the back angles. The components of the above particle spectra emitted at forward angles are interpreted in terms of a direct-interaction mechanism on "α clusters" in the surface, and a Monte Carlo calculation was performed to compute the yield of "α clusters" knocked out by prompt cascade nucleons. The tritons and 3He particles might partly be ejected by a double pickup process, partly by a stripping mechanism on "α clusters."