ILC (International Linear Collider) is e+ e- linear collider in the next high energy program promoted by ICFA. In ILC, an intense positron pulse in a multi-bunch format is generated with gamma ray from Undulator radiation. As a technical backup, the electron driven positron source has been studied. By employing a standing wave L-band accelerator for the capture linac, an enough amount of positron can be captured due to the large aperture, even with a limited accelerator gradient. However, the heavy beam loading up to 2 A perturbs the field gradient and profile along the longitudinal position. We present the capture performance of the ILC positron source including the heavy beam loading effect.