Catalyst degradation diagnosing device

The invention is aimed at providing a catalyst degradation diagnosing device which is capable of correctly diagnosing degradation of an oxidizing catalyst loaded on a particle filter. The invention adopts the following implementation mode: when a predetermined quantity of fuel is supplied to an OCF which is formed when the oxidizing catalyst is loaded on the particle filter, the degradation of the catalyst loaded on the OFC is performed according to a physical quantity relevant to heat generated in the OCF; in the degradation diagnosing device performing degradation diagnosing operation, whether PM oxidizing reaction takes place in the OFC is determined when the predetermined quantity of fuel is supplied to the OCF; if the PM oxidizing reaction takes place in the OFC, the degradation diagnosing operation is not performed; if the PM oxidizing reaction does not take place in the OFC, the degradation diagnosing operation is performed. 本发明的课题在于，提供种催化剂的劣化诊断装置，其对具有氧化功能并且被负载于颗粒过滤器上的催化剂的劣化正确地进行诊断。本发明采用了如下实施方式，即，在向将氧化