Flux and solder paste

Provided is a flux capable of obtaining predetermined rheological characteristics both at room temperature and under a thermal history that is assumed for soldering and capable of suppressing the amount of a residue after soldering to realize a low residue. The flux contains a first alcohol compound that has two or more OH groups and has a melting point of lower than 25° C. and a second alcohol compound that has two or more OH groups and has a melting point of higher than 25° C., the first alcohol compound is glycerin, the second alcohol compound is 2,5-dimethylhexane-2,5-diol, the flux has a viscosity of 10 Pa·s or more and 50 Pa·s or less at 25° C. and has a viscosity of more than 0 Pa·s and 1 Pa·s or less at 100° C., and, in a case where 10 mg of the flux is heated up to 25° C. to 250° C. under a N2 atmosphere at a temperature rise rate of 10° C./min, the weight of the flux after heating is 15% or less of the weight of the flux before heating.