A sludge treatment method allowing an improvement in a phosphorus recovery rate and sludge volume reduction by efficiently eluting phosphorus in the sludge. The sludge treatment method includes: a step of foaming a sludge-containing liquid by blowing an ozone-containing gas into the sludge-containing liquid; and a step of eluting phosphorus in the sludge-containing liquid by bringing sludge adsorbed on bubbles and a sludge-dissolving agent into contact with each other. The sludge treatment method may further include the steps of: separating the phosphorus eluted sludge-containing liquid into a phosphorus eluate and a residual sludge; and precipitating a phosphorus compound by adding a coagulant to the separated phosphorus eluate.