A multi-layer video decoding method includes receiving a plurality of multi-layer image streams that constitute a multi-layer video, obtaining, from a data unit header including information of a second random access point (RAP) picture that corresponds to a first RAP picture included in a first layer image stream and is included in a second layer image stream from among the plurality of multi-layer image streams, first picture order count (POC) information for determining a first partial value of a POC of the second RAP picture that is set to be the same as a POC of the first RAP picture, obtaining, from the data unit header, second POC information about a second partial value of the POC of the second RAP picture, and obtaining the POC of the second RAP picture by using the first POC information and the second POC information.