We have identified a very interesting Ly \alpha emitter , whose Ly \alpha emission line has an extremely large observed equivalent width of EW _ { 0 } = 436 ^ { +422 } _ { -149 } Å , which corresponds to an extraordinarily large intrinsic rest-frame equivalent width of EW _ { 0 } ^ { int } = 872 ^ { +844 } _ { -298 } Å after the average intergalactic absorption correction . The object was spectroscopically confirmed to be a real Ly \alpha emitter by its apparent asymmetric Ly \alpha line profile detected at z = 6.538 . The continuum emission of the object was definitely detected in our deep z ^ { \prime } -band image ; thus , its EW _ { 0 } was reliably determined . Follow-up deep near-infrared spectroscopy revealed emission lines of neither He ii \lambda 1640 as an apparent signature of Population III , nor C iv \lambda 1549 as a proof of active nucleus . No detection of short-lived He ii \lambda 1640 line is not necessarily inconsistent with the interpretation that the underlying stellar population of the object is dominated by Population III . We found that the observed extremely large EW _ { 0 } of the Ly \alpha emission and the upper limit on the EW _ { 0 } of the He ii \lambda 1640 emission can be explained by population synthesis models favoring a very young age less than 2 - 4 Myr and massive metal-poor ( Z < 10 ^ { -5 } ) or even metal-free stars . The observed large EW _ { 0 } of Ly \alpha is hardly explained by Population I/II synthesis models with Z \geq 10 ^ { -3 } . However , we can not conclusively rule out the possibility that this object is composed of a normal stellar population with a clumpy dust distribution , which could enhance the Ly \alpha EW _ { 0 } , though its significance is still unclear .