The plasma generator (hereinafter referred to as the “plasma generator according to Example 1”), in which the above dimensions are adopted, the dielectric substrate 12 is made of alumina, the high-voltage electrode 14 is made of conductive materials including copper as a primary material, and the low-voltage electrode 20 is made of copper, was operated to generate plasma with flowing gas while applying a voltage on the following conditions.

Applied voltage: 7.6 kVpp, Frequency 38 kHz, Gas type: nitrogen, Gas flow rate 300 L/min

[Verification of Uniform Plasma Jet]

FIG. 5 is a plan view in which polypropylene (PP) films as objects to be irradiated are placed on a stage at predetermined intervals. As shown in FIG. 5, the polypropylene (PP) films were placed on the stage as the objects to be irradiated at the predetermined intervals, and was irradiated with plasma from above using the plasma generator according to Example 1. The PP films were fixed on a uniaxial stage at a position 2 mm (irradiation distance) apart from the blowout outlet, and were irradiated with plasma by allowing the blowout outlet to conduct reciprocating motions at a speed of 100 mm/sec. The water contact angle on the surface of each PP film was measured after the twice irradiation (after the twice reciprocating motions), after the 10 times irradiation (after the 10 times reciprocating motions), and after 200 times irradiation (after the 200 times reciprocating motions). The water contact angle was measured as follows. The water contact angle was measured under the following conditions. Contact angle meter: DMs-401 (Kyowa Interface Science Co., Ltd), Liquid volume: 2 μL, Approximation by elliptical fitting.