INTERNAL COMBUSTION ENGINE EXHAUST PURIFICATION DEVICE

A hydrocarbon supply valve (15) and an exhaust gas purification catalyst (13) are arranged in the engine exhaust gas passage of an internal combustion engine. The exhaust gas purification catalyst (13) comprises an upstream catalyst (14a) and a downstream catalyst (14b) arranged in series, and the upstream catalyst (14a) forms a circular truncated cone widening towards the downstream catalyst (14b). The concentration of hydrocarbons flowing into the upstream catalyst (14a) oscillates at an amplitude within a pre-set range of 200ppm or greater and at a period within a pre-set range of 5 seconds or less, thereby reducing the NO_x contained in the exhaust gas in the exhaust gas purification catalyst (13).