TWI773934B

Provided is a methacrylic acid production device which has excellent continuous workability. The methacrylic acid production device (100) is provided with: a first reactor (10) for obtaining methacrolein; a second reactor (20) for obtaining methacrylic acid; a methylacrolein recovery unit (70); a line (LA) connecting the outlet (10j) of the first reactor (10) and the inlet (20i) of the second reactor (20); a line (LB) connecting the line (LA) and the oxygen supply source; a line (LC) connecting the outlet (20j) of the second reactor (20) and the liquid inlet (70i) of the methylacrolein recovery unit (70); and a line (LD) connecting the gas outlet (70gj) of the methylacrolein recovery unit (70) and the line (LA). The line (LD) has a heating unit (23a) that is disposed on at least a portion of the line between the gas outlet (70gj) and a position where the line length is 30, where the line length from the gas outlet (70gj) to a connection portion (Xo) with the line (LA) is set as 100.