Provided is a movement assistance device that is capable of causing a movement to be performed more safely during blood purification treatment. A movement assistance device that can assist movements performed by a patient during blood purification treatment, wherein said movement support device includes: an estimation line generation means 4 that, after the start of blood purification treatment, generates an estimation line on the basis of the rate of change in the circulating blood volume (ΔBV), which is a parameter related to a change in circulating blood volume of a patient that is continuously measured before the start of movement, said estimation line estimating the transition in the rate of change in the circulating blood volume (ΔBV) after the start of movement； a first calculation means 5 that calculates the difference or ratio between a measured value of the rate of change in the circulating blood volume (ΔBV) of a patient after the start of movement during blood purification treatment and a value of the estimation line generated by the estimation line generation means 4； and a first monitoring means 6 that monitors whether or not the difference or the ratio calculated by the first calculation means 5 exceeds a threshold value that is set in advance.L'invention concerne un dispositif d'assistance au mouvement qui est apte à amener la réalisation d'un mouvement de manière plus sûre pendant un traitement de purification de sang. L'invention concerne un dispositif d'assistance au mouvement qui peut assister des mouvements effectués par un patient pendant un traitement de purification de sang, ledit dispositif de support de mouvement comprenant : un moyen de génération de ligne d'estimation (4) qui, après le début du traitement de purification de sang, génère une ligne d'estimation sur la base du taux de changement du volume de sang circulant (ΔVS), qui est un paramètre lié à un changement du volume de sang circulant d'un patient qui est mesuré en continu avant
