Provide an electrode catalyst with excellent catalytic activity that can contribute to cost reduction of PEFC. The electrode catalyst includes a hollow carbon carrier with mesopores with a pore size of 2 to 50 nm and a catalyst particle supported on the carrier. The catalyst particle is supported on both inside and outside the mesopores of the carrier, and have a core portion formed on the carrier and a shell portion covering at least a part of the surface of the core portion. Pd is included in the core portion, and Pt is included in the shell portion, and when the analysis of the particle size distribution of the catalyst particles using the three dimensional reconstructed image obtained by electron beam tomography (electron tomography) measurement using an STEM is performed, the ratio of the catalyst particles supported inside the mesopore is 50% or more.