A wafer transfer apparatus is provided. In a minimum transformed state where a robot arm is transformed such that a distance defined from a pivot axis to an arm portion, which is farthest in a radial direction relative to the pivot axis, is minimum, a minimum rotation radius R, is set to exceed ½ of a length B in the forward and backward directions of an interface space, the length B corresponding to a length between the front wall and the rear wall of the interface space forming portion, and is further set to be equal to or less than a subtracted value obtained by subtracting a distance L0 in the forward and backward directions from the rear wall of the interface space forming portion to the pivot axis, from the length B in the forward and backward directions of the interface space (i.e., B / 2<R≦B−L0).