A method of manufacturing a thin-film magnetic head works a part to be worked to a target length by carrying out an etching process on an object to be worked using an etching apparatus. The method carries out a measuring process that measures a length before working of a part to be worked using a measuring apparatus and a calculation process that calculates the processing time of the etching process required to work the part to be worked from the length before working to the target length based on a first calculation result correcting parameter obtained in advance corresponding to the measuring apparatus, a second calculation result correcting parameter obtained in advance corresponding to a position of the part to be worked, a third calculation result correcting parameter obtained in advance corresponding to a value of a current supplied to an electrode of the etching apparatus during the etching process, a fourth calculation result correcting parameter obtained in advance corresponding to a total usage time of the electrode, the length before working, and the target length. The etching process is carried out on the object to be worked for the calculated processing time.