According to one embodiment, an IP broadcast system includes a transmitting side and a receiving side connected to the transmitting side through a broadcast network on an IP network. The transmitting side includes a multiplexer which generates a standardized multiplex frame including at least a header field and an information field by multiplexing a plurality of RTP packets. The receiving side includes a buffer which temporarily holds the multiplex frame from the broadcast network and a program reproducer which retrieves and analyzes the multiplex frame from the buffer, extracts a reproduction clock shared by a plurality of programs, demultiplexes a plurality of TSs for each program from the multiplex frame, and based on the reproduction clock, reproduces the programs from each TS.