matter, it is found that the energy per baryon of SQM is lower than that of the normal nuclear matter for a rather wide range of QCD parameters[@b71; @w84; @fj84]. Assuming SQM is absolutely stable at zero pressure, strange stars, which almost completely consist of SQM, could exist in nature[@afo86; @hzr86]. The assumption is [*strong*]{}, but not impossible. Therefore many objects which were previously believed to be neutron stars, including radio pulsars, might actually be strange stars. In fact, more and more strange star candidates have been proposed recently in the literatures[@ldw95lbddv99; @bom97; @cdwl98; @xqz99], including both the accretion-powered and the rotation-powered compact objects.

Therefore, we have to think over a question again, which appeared to have been answered, “What is the nature of pulsars?” In their pioneering work, Alcock et al.[@afo86] have suggested that radio pulsars might be strange stars. However, they did not fully discuss the possible observational consequences of such a strange star idea. Nor was this done by the later authors. What if pulsars are born as strange stars? How well can a strange star model interpret the pulsar observational data as compared with a neutron star model? Is there any criterion based on the radiation 