PURPOSE: To keep temperature of all the cavities in a mold equal by a simple device by a method wherein specific ladder passages are engraved in an injection mold or a temperature adjusting mold having a plurality of cavities at fixed intervals to pass heat medium through said passages.

CONSTITUTION: Two main passages 5, 6 are engraved at positions across the sides of each cavity 4, 4 on the projecting surfaces of each split mold 1a, 1a of an injection mold or the temperature adjusting mold 1 having a plurality of cavities 4, 4 and an inlet 5a and an outlet 6a are provided by closing one end of each main passage alternately. The foregoing main passages 5, 6 are connected by prescribed numbers of longitudinal bypasses 7, 7 engraved in the middle part between the cavities 4, 4 to form a ladder passage. Heat medium is supplied from the inlet 5a, branched into each bypass 7 and keeps the mold temperature uniform.