A weight measuring device comprises a load detecting section for constantly detecting a load value (W) of a sample placed on a measuring pan; a moving average processing section for calculating a moving average (Wa) of the detected load value (W); a load changing rate calculating section for calculating a load changing rate per unit time (Wb) of the detected load value (W); a storage section for storing a first load change threshold (Wr1), a second load change threshold (Wr2) which is smaller than the first load change threshold (Wr1) and a load changing rate threshold per unit time (Wt); a determining section for determining whether a moving average processing should be executed; and a weight conversion processing section for calculating a weight of the sample from the load (W) or the moving average (Wa).