An electrode assembly of a plasma processing apparatus that enables damage to an electrode plate to be prevented, and enables an increase in the number of parts to be prevented so that a worsening of the ability to carry out maintenance can be prevented. An upper electrode assembly has an upper electrode plate 32, a cooling plate (C/P) 34 and a spacer 37 interposed between the upper electrode plate 32 and the C/P 34. The upper electrode plate 32 has therein electrode plate gas-passing holes 32a that penetrate through the upper electrode plate 32. The C/P 34 has therein C/P gas-passing holes 34a that penetrate through the C/P 34. The spacer 37 has therein spacer gas-passing holes 37a that penetrate through the spacer 37. The electrode plate gas-passing holes 32a, C/P gas-passing holes 34a and the spacer gas-passing holes 37a are not disposed collinearly.