NOVELTY - The method involves storing process liquid in a processing tank. A substrate is accommodated in an inner tank. The process liquid overflowing from the inner tank is collected in an outer tank. Presence or absence of abnormality in supply is judged by comparing performance values (AV2). An ejection pipe and a discharge port are connected with a supply piping. A pump, an in-line heater, a filter, and a density detection part are sequentially attached to the supply piping from a discharge port side. Transmitted-light intensity of the process liquid is detected by the density detection part.    USE - Method for detecting abnormality during supply of chemical solution e.g. process liquid such as sulfuric acid/hydrogen peroxide liquid mixture (SPM), to a substrate in a substrate processing apparatus. Uses include but are not limited to a semiconductor wafer, LCD substrate, plasma display substrate, organic electroluminescence (EL) substrate, field emission display (FED) substrate, optical display substrate, magnetic disk substrate, magneto optical disk substrate, photomask substrate and solar cell substrate.    ADVANTAGE - The presence or absence of abnormality in the supply is judged by comparing the performance values even if replenishment frequency of chemical solution differs based on elapsed time after the process liquid is generated, thus separately setting monitoring intervals after the process liquid is generated until generating new process liquid into a time slot, and hence detecting abnormality in supply in an appropriate manner.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a substrate processing apparatus comprising a processing tank.    DESCRIPTION OF DRAWING(S) - The drawing shows a timing chart illustrating an operation of supply abnormality detection by a substrate processing apparatus.'(Drawing includes non-English language text)'    Performance values (AV1, AV2)    Normal values (IV1, IV2)    Disregard time (T1)    Monitoring intervals (TI1, TI2)    Time slots (TZ1, TZ2)