Abstract: The present invention relates to a method of detecting a degassed state in a mold and a system therefor. A gas release opening is formed between a movable mold part and stationary mold part, and a diffuser block having a path for releasing the gas to atmosphere is disposed on the mold. A secondary flow path capable of generating a secondary flow when the gas is released is formed in this diffuser block, and a wind velocity sensor is disposed in this path. Wind velocities of the secondary flow, which are detected by the wind velocity sensor, serve as indications of a cast state and the like in a die cast machine or the like. The secondary flow path is suitably shut off by a shut-off mechanism, and connected to an air cleaner, so that the wind velocity sensor can be effectively protected from dust and the like.