An encoder includes circuitry and memory connected to the circuitry. The circuitry, in operation: splits one picture included in pictures into areas, intra encodes the entirety of an area among the areas; and switches areas to be intra encoded for each picture included in the pictures. In at least one of (i) generation of a reference pixel in inter prediction or (ii) loop filtering, only pixels in the area intra encoded or pixels in an area which precedes the area intra encoded in coding order are used among pixels included in the pictures.