To provide a variable-cylinder internal combustion engine in which combustibility in a cylinder recovered from a deactivated state to an operation state is improved by inhibiting piston temperature from dropping during a cylinder-deactivation operation. The variable-cylinder internal combustion engine comprises an oil-jet 41 for cooling a piston by spraying oil on the piston, and a cylinder-deactivation control means for switching the operation mode between the whole-cylinder operation and a deactivation cylinder operation. The oil-jet 41 sprays the oil solely on a piston 11a of a full-time operated cylinder C1. Thus, at the time when the operation-mode has been shifted from the whole-cylinder operation to a deactivation cylinder operation, temperature of a piston 11b in a cylinder C4 which is deactivated in a deactivation operation is inhibited from dropping. Consequently, at a point of time when the operation is recovered from a deactivation cylinder operation to the whole-cylinder operation, the piston 11b is held at a high temperature, and combustibility in the cylinder C4 which is recovered from the deactivated state to an operation state is improved.