The performance of a force feedback system is disturbed by delay that arises from the time required for transmission and processing of data. We used a psychophysical method to measure how much a user's subjective impression of elasticity associated with delays of feedback force deviated from the original physical elasticity. The results show that users' point of subjective equality (PSE) for their subjective impression of elasticity decreased as the delay of feedback force increased. We proposed a model that estimates the PSE of elasticity from the variables that can be physically measured. Another experiment was conducted to examine the model's prediction, which the results supported.