Apparatus for producing lower olefin-containing gas and method for producing lower olefin-containing gas

In an apparatus, a gas containing CH4 and CO2 is supplied from a first supply unit to a synthetic gas production unit which generates a synthetic gas containing CO and H2 while heating a first catalytic structure; the synthetic gas is supplied to a gas production unit which generates a lower olefin-containing gas including propylene while heating a second catalytic structure; and a detection unit detects propylene discharged from the gas production unit. The first catalytic structure includes first supports having a porous structure and a first metal fine particle that is present in first channels of the first supports. The second catalyst structure includes second supports having a porous structure and a second metal fine particle in the second supports. The second supports have a second channels, a portion of which have an average inner diameter of 0.95 nm or less.