The present invention relates to a composite semipermeable membrane including: a support membrane; and a separation functional layer provided on the support membrane, in which the separation functional layer includes a thin membrane, the thin membrane has a fold structure including a plurality of protrusions, an actual length L of the thin membrane per 1 μm length of the support membrane in a cross-sectional direction perpendicular to a membrane surface is 3.0 μm or more, and a thickness of the thin membrane in the protrusion is 15 nm or more.