Abstract: The present invention relates to a catalyst which is a composite oxide including at least one element X selected from the group consisting of elements belonging to Groups 3 to 6 of the periodic table, and at least one element Z selected from the group consisting of elements belonging to Group 14 of the periodic table, wherein the catalyst has mesopores.

Abstract: A catalyst for synthesizing a conjugated diene from a raw material including an alcohol, which includes at least Ce and Zn as metal elements constituting the catalyst. An apparatus for producing a conjugated diene, including: a reaction tube (1) provided with the catalyst; a supply means for supplying a raw material gas containing the raw material into the reaction tube (1); and an outlet means for releasing a product from the reaction tube (1). A method for producing a conjugated diene, including contacting a raw material gas containing a raw material with the catalyst to obtain a conjugated diene. The amount of the raw material is preferably 10 to 50% by volume (in terms of gas volume) with respect to 100% by volume (in terms of gas volume) of the raw material gas.