Disclosed are a Mo—Bi—Nb—Te based composite metal oxide; and a process for producing (meth)acrylic acid from at least one reaction material selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, wherein the Mo—Bi—Nb—Te based composite metal oxide is used as a catalyst. Also, disclosed is a process for producing (meth)acrylic acid comprising a first step of producing (meth)acrolein as a main product from at least one reaction material selected from the group consisting of propylene, propane, isobutylene, t-butyl alcohol and methyl-t-butyl ether, and a second step of producing (meth)acrylic acid from the (meth)acrolein, wherein yield of (meth)acrylic acid in the product of the first step is 20 mole % or higher.