A phase shifting mask is used for manufacturing a semiconductor integrated circuit device including a conductor pattern in which the line width of patterned conductor strips or the space between patterned conductor strips is not constant. For main transparent areas in the mask corresponding to the conductor pattern, auxiliary pattern segments are provided for compensating changes in the phase distribution of transmitted light caused by changes of the line width or the space. Alternately, the spaces between the conductor strips are adjusted to suppress the changes in the phase distribution of transmitted light. Whether the auxiliary pattern segments should have the phase shifting function is determined depending upon the disposition of the main transparent areas.