EXHAUST GAS CLEANER FOR INTERNAL COMBUSTION ENGINE

In an internal combustion engine (100) provided with an NOx absorbing reduction catalyst (2) in an exhaust gas passage (1), there are arranged: an oxygen sensor (3) which is mounted downstream of the NOx absorbing reduction catalyst (2) in the exhaust gas passage (1); and a determination means for determining a condition of degradation of the NOx absorbing reduction catalyst (2) on the basis of a time length, during which a voltage value, having a small amount of variation before the voltage value outputted from the oxygen sensor (3) is recorded as a maximum value when executing a rich spike, is recorded.