A cooling structure for electronic devices includes a plurality of electronic device accommodating boxes, in which electronic devices are accommodated, disposed in a casing in multiple stages. A vent portion which allows ventilation between the inside and the outside of the casing is formed in a ceiling of the casing. In a first accommodating portion for accommodating the first electronic device accommodating box which is defined at the stage close to the ceiling, a hollow duct having two opening faces is arranged. The first opening face faces the vent portion and the second opening face faces a second accommodating portion for accommodating the second electronic device accommodating box which is defined at the stage remote from the ceiling. Air inside the second electronic device accommodating box is discharged through the inside of the duct. Air inside of the first electronic device accommodating box is discharged from the vent portion.