A sludge condensing machine includes: a gravity filtration section conducting a gravity filtering to a sludge while conveying the sludge on an upper surface of a filtration body, and a movement mechanism, disposed at a downstream side of a sludge insertion position of the gravity filtration section, for reducing a dimension of the sludge in a width direction on the filtration body by moving the sludge in a direction intersecting a conveying direction that the sludge is conveyed by the filtration body.