An estimation device comprising: an acquisition unit configured to: acquire a first pipe surface temperature and a second pipe surface temperature, wherein the first pipe surface temperature is an outer surface temperature of a pipe at a precipitate generation position at which a precipitate is adhered to an inner surface of the pipe through which a fluid flows, and the second pipe surface temperature is the outer surface temperature of the pipe at a reference position different from the precipitate generation position; a calculation unit configured to calculate an in-pipe fluid temperature that is a temperature of the fluid at the precipitate generation position based on the second pipe surface temperature; and an estimation unit configured to estimate a thickness of the precipitate based on the in-pipe fluid temperature and the first pipe surface temperature, wherein in a case where the precipitate is not adhered to the inner surface at the reference position, the estimation unit is configured to estimate the thickness of the precipitate at the precipitate generation position, the acquisition unit is further configured to acquire a heat insulating material surface temperature that is an outer surface temperature of a heat insulating material that covers the pipe, the calculation unit is configured to calculate the in-pipe fluid temperature based on the second pipe surface temperature, the heat insulating material surface temperature, and thermal resistance of each of the fluid, the pipe, and the heat insulating material, and the estimation unit is configured to estimate the thickness of the precipitate at the precipitate generation position based on a thickness distribution of the precipitates that are associated with the in-pipe fluid temperature and the first pipe surface temperature. acquire a first pipe surface temperature and a second pipe surface temperature, wherein the first pipe surface temperature is an outer surface temperature of a pipe at a precipitate generation position at which a precipitate is adhered to an inner surface of the pipe through which a fluid flows, and the second pipe surface temperature is the outer surface temperature of the pipe at a reference position different from the precipitate generation position; a calculation unit configured to calculate an in-pipe fluid temperature that is a temperature of the fluid at the precipitate generation position based on the second pipe surface temperature; and an estimation unit configured to estimate a thickness of the precipitate based on the in-pipe fluid temperature and the first pipe surface temperature, wherein in a case where the precipitate is not adhered to the inner surface at the reference position, the estimation unit is configured to estimate the thickness of the precipitate at the precipitate generation position, the acquisition unit is further configured to acquire a heat insulating material surface temperature that is an outer surface temperature of a heat insulating material that covers the pipe, the calculation unit is configured to calculate the in-pipe fluid temperature based on the second pipe surface temperature, the heat insulating material surface temperature, and thermal resistance of each of the fluid, the pipe, and the heat insulating material, and the estimation unit is configured to estimate the thickness of the precipitate at the precipitate generation position based on a thickness distribution of the precipitates that are associated with the in-pipe fluid temperature and the first pipe surface temperature. <EOS>