To provide an exhaust gas purification catalyst device capable of increasing the exhaust gas purification efficiency of an NOx storage catalyst having an O2 storage function without worsening fuel economy.

A precious metal 36 and the NOx storage catalyst which stores NOx in an exhaust gas when an exhaust gas air-fuel ratio is lean and releases the stored NOx when the exhaust gas air-fuel ratio is stoichiometric or rich to reducing treatment and an oxygen storage agent 34 are carried on the carrying layer of the exhaust gas purification catalyst device 30. The supported amount of the oxygen storage agent is set smaller in the exhaust gas passage upstream side area 32a of a carrier than in the exhaust gas passage downstream side area 32b.