Pile coupler

The present invention relates to a pile coupler which does not use any concrete for the foundation when building piles to support a structure such as a solar power generation structure and enables the jointing work on areas connecting pipes respectively arranged on the upper and lower part quickly. According to the present invention, the pile coupler is used to connect two piles having different diameters. The pile coupler includes: a round unit having a cross-section in a semi-circular shape; and a flat plate unit which has bolt holes formed in the length direction to respectively protrude from both ends of the round unit in the semi-circular shape to the outside. The round unit includes: a large diameter unit formed to have a predetermined length; a small diameter unit which has another predetermined length smaller than that of the large diameter unit; and a tilted unit which connects and integrates the large diameter unit and the small diameter unit. Each of the large diameter unit and the small diameter u