To provide a molding die for sealing a resin controlling a demolding balance when demolding a work form the molding die after sealing the resin and its surface treating method.

A hard chrome plating for example of a friction coefficient of 0.8 is applied to the surface of a first metal surface 3 and a chrome nitride plating for example of a friction coefficient of 0.5 is applied to the surface of a second metal surface 4 as a surface treatment for enhancing demoldability on the surfaces of the first and second mold cavities 5, 6 from which the work is required to be demolded, thereby the work can be taken out without depending on the mechanical ejector by changing the demolding resistance of the work, a mold structure can be simplified by changing the balance of the friction resistance of the first metal surface 3 and the second metal surface 4 even in the case that mechanical demolding is difficult, designing of the mold can be easily done, a complicated ejector mechanism can be simplified to be able to provide inexpensive molds.