A resistance spot welding method of squeezing parts to be welded by a pair of electrodes, and passing a current while applying an electrode force to join the parts to be welded, the parts to be welded being a plurality of overlapping metal sheets, the resistance spot welding method comprising: a first step of passing a current by constant current control to form a fusion zone having a diameter of not less than 2√t, expressed in mm, between the metal sheets, where t, expressed in mm, is a sheet thickness of a thinnest metal sheet of the metal sheets; and a second step of cooling the fusion zone to at least partially solidify the fusion zone, wherein a diameter of a molten portion of the fusion zone is not greater than 80 % of D, where D, expressed in mm, is a diameter of the fusion zone formed in the first step, and wherein a cooling time C2, expressed in ms, during which current passage is stopped, satisfies C2 ≥ 20 · t0/R, where t0 is a total thickness, expressed in mm, of the parts to be welded and R is the electrode tip diameter, expressed in mm; characterized by a third step of performing adaptive control welding by controlling a current passage amount according to a target that is set, wherein test welding for setting the target is performed beforehand, in the test welding, first to third test steps corresponding to the first to the third steps are performed by constant current control, to derive a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume at least in the third test step, and in the third step, the target is set to the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume that are derived in the third test step, adaptive control welding is performed using the time variation curve as the target, and, the current passage amount is controlled in order to compensate for a difference of an amount of time variation of an instantaneous amount of heat generated per unit volume in the third step from the time variation curve within a remaining welding time in the third step so that a cumulative amount of heat generated in the third step matches the cumulative amount of heat generated that is derived beforehand in the third test step. a first step of passing a current by constant current control to form a fusion zone having a diameter of not less than 2√t, expressed in mm, between the metal sheets, where t, expressed in mm, is a sheet thickness of a thinnest metal sheet of the metal sheets; and a second step of cooling the fusion zone to at least partially solidify the fusion zone, wherein a diameter of a molten portion of the fusion zone is not greater than 80 % of D, where D, expressed in mm, is a diameter of the fusion zone formed in the first step, and wherein a cooling time C2, expressed in ms, during which current passage is stopped, satisfies C2 ≥ 20 · t0/R, where t0 is a total thickness, expressed in mm, of the parts to be welded and R is the electrode tip diameter, expressed in mm; characterized by a third step of performing adaptive control welding by controlling a current passage amount according to a target that is set, wherein test welding for setting the target is performed beforehand, in the test welding, first to third test steps corresponding to the first to the third steps are performed by constant current control, to derive a time variation curve of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume at least in the third test step, and in the third step, the target is set to the time variation curve of the instantaneous amount of heat generated per unit volume and the cumulative amount of heat generated per unit volume that are derived in the third test step, adaptive control welding is performed using the time variation curve as the target, and, the current passage amount is controlled in order to compensate for a difference of an amount of time variation of an instantaneous amount of heat generated per unit volume in the third step from the time variation curve within a remaining welding time in the third step so that a cumulative amount of heat generated in the third step matches the cumulative amount of heat generated that is derived beforehand in the third test step.