Endoscope objective optical system and endoscope

An endoscope objective optical system comprising in order from an object side:

• a front group having a positive refractive power;
• an aperture stop;
• and
• a rear group having a positive refractive power, wherein
• the front group includes a negative lens which is nearest to an object,
• the rear group includes a positive lens which is nearest to an image,
• the negative lens has a planoconcave shape with a flat surface directed toward the object side, and
• the endoscope objective optical system satisfies following conditional expressions (1″′), (2), and (3″′)
• −15.0<ff/f1<−4.2 (1″′)
• −1.70<f1/f<−0.95 (2)
• 0.6<g1/g2<1.20 (3″′)
• where,
• ff denotes a focal length of the positive lens,
• f1 denotes a focal length of the negative lens,
• f denotes a focal length of the overall endoscope objective optical system,
• g1 denotes a focal length of the front group, and
• g2 denotes a focal length of the rear group.