The invention provides a device and a method for detecting condition of molds (m1, m2) attached to an injection molding machine with low cost and high reliability. A load exerted on a product ejecting mechanism (7) or a mold opening/closing mechanism (4, 5, m1, 6) is preferably estimated by a disturbance torque estimating observer. An index value (for example a maximum value or average value) of the load is obtained and stored preferably in each molding cycle of the injection molding machine. Obtained values of the index are suitably displayed as a graph on a display device to indicate variation of the load in time series and thus allow an operator to monitor the condition of the molds.