We have investigated the γd → π0π0d reaction to study dibaryon resonances. The total cross section as a function of the γd center-of-mass energy shows resonance-like behavior peaked at around 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by kinematics for quasi-free π0π0 production with deuteron coalescence. A clear peak is observed at 2.14 GeV in the π0d invariant-mass distributions. The present work shows a sequential process γd → RIS → π0RIV → π0π0d is dominant with two 2.47- and 2.63-GeV isoscalar dibaryons (RIS) and a 2.14-GeV isovector dibaryon (RIV).