A thermal base generator, comprising an acidic compound which is an ammonium salt containing a carboxylic acid anion having a pKa1 of 0-4 and an ammonium cation, wherein (a) the carboxylic acid anion - is of the Formula EWG-C(=O)-O ⊝, wherein EWG is an electron-withdrawing group selected from (EWG-1) to (EWG-6): wherein R x1 -R x3 each independently are H, alkyl, alkenyl, aryl, hydroxyl or carboxyl, and Ar is an aromatic ring group; or - is a di- or higher-valent, preferably a divalent, anion of carboxylic acid having two or more carboxyl groups, more preferably an anion of the formula: wherein L 10 is a single bond, or a divalent linking group selected from alkylene, alkenylene, arylene, -NR X - and a combination thereof, and R X is H, alkyl, alkenyl or aryl, and particularly preferably is selected from a maleic acid anion, a phthalic acid anion, an N-phenyliminodiacetic acid anion and an oxalic acid anion; and (b) the ammonium cation is of the formula (Y1-1) or (Y1-2): wherein R 101 is an n-valent organic group, R 102 -R 106 each independently are H or a hydrocarbon group, R 150 is a hydrocarbon group, and R 104 and R 105, and R 104 and R 150 may be bonded to each other to form a ring, and n is an integer of ≥ 1, and preferably the ammonium cation is of the formula (Y1-1) or (Y1-2) wherein R 101 is an aromatic ring group. (a) the carboxylic acid anion - is of the Formula EWG-C(=O)-O ⊝, wherein EWG is an electron-withdrawing group selected from (EWG-1) to (EWG-6): wherein R x1 -R x3 each independently are H, alkyl, alkenyl, aryl, hydroxyl or carboxyl, and Ar is an aromatic ring group; or - is a di- or higher-valent, preferably a divalent, anion of carboxylic acid having two or more carboxyl groups, more preferably an anion of the formula: wherein L 10 is a single bond, or a divalent linking group selected from alkylene, alkenylene, arylene, -NR X - and a combination thereof, and R X is H, alkyl, alkenyl or aryl, and particularly preferably is selected from a maleic acid anion, a phthalic acid anion, an N-phenyliminodiacetic acid anion and an oxalic acid anion; and - is of the Formula EWG-C(=O)-O ⊝, wherein EWG is an electron-withdrawing group selected from (EWG-1) to (EWG-6): wherein R x1 -R x3 each independently are H, alkyl, alkenyl, aryl, hydroxyl or carboxyl, and Ar is an aromatic ring group; or - is a di- or higher-valent, preferably a divalent, anion of carboxylic acid having two or more carboxyl groups, more preferably an anion of the formula: wherein L 10 is a single bond, or a divalent linking group selected from alkylene, alkenylene, arylene, -NR X - and a combination thereof, and R X is H, alkyl, alkenyl or aryl, and particularly preferably is selected from a maleic acid anion, a phthalic acid anion, an N-phenyliminodiacetic acid anion and an oxalic acid anion; and (b) the ammonium cation is of the formula (Y1-1) or (Y1-2): wherein R 101 is an n-valent organic group, R 102 -R 106 each independently are H or a hydrocarbon group, R 150 is a hydrocarbon group, and R 104 and R 105, and R 104 and R 150 may be bonded to each other to form a ring, and n is an integer of ≥ 1, and preferably the ammonium cation is of the formula (Y1-1) or (Y1-2) wherein R 101 is an aromatic ring group. R 101 is an n-valent organic group, R 102 -R 106 each independently are H or a hydrocarbon group, R 150 is a hydrocarbon group, and R 104 and R 105, and R 104 and R 150 may be bonded to each other to form a ring, and n is an integer of ≥ 1,