To provide an insulating sheet form and an insulating method realizing reduction in the number of components and reduction in assembly man-hours, and capable of fixing simply and steadily.

The insulating sheet form has a projection part and a cut-out part provided, and after surrounding the surroundings of insulated object including a main substrate 301 as a start, the projecting part is engaged with the cut-out part. In the insulating method, when the projecting part cannot be installed in the insulating sheet, a second insulated member starting from, such as, a check pad 402 formed at the projecting part is engaged with the cut-out part formed in the insulating sheet. Even when the projecting part can be formed in the insulating sheet, a second insulated member such as a check pad 402 is inserted into the engaging part of the projecting part and the cut-out part provided in the insulating sheet.