In a process of producing syngas by heating and gasification of a fuel such as coal, an absorbent reduces halogen compound gas leakage in the presence of high-temperature, high-concentration steam into subsequent processes. This invention relates to a halogen compound absorbent which contains 30-90 mass% of a basic calcium compound and 10-70 mass% of a non-calcium metal compound and/or clay minerals, and relates to a method of producing syngas using said absorbent.