PROBLEM TO BE SOLVED: To provide a technology for casting a cast steel to which a full mold process can be applied as a method of casting the cast steel.SOLUTION: A mold is used for casting a product made of a cast steel by pouring the melted cast steel through a runner into a casting sand in which an evaporative pattern is buried. The mold includes: a flask having a sealed structure; a negative pressure-generating source that communicates with a lower part of the flask through a discharge pipe and is provided so as to suck in decomposed gas generated due to the disappearance of the evaporative pattern during casting and to discharge the gas to the outside of the flask; an air-sending pipe, arranged on an upper portion of the evaporative pattern, for supplying an outside air to the inside of the flask; and an exhaust air duct provided on the upper portion of the evaporative pattern, while the whole of the air duct is buried in the casting sand. The mold is configured such that the outside air having a high temperature can be supplied to the evaporative pattern through the air-sending pipe while decompressing the flask via the negative pressure-generating source.