Provided is an endoscope objective optical system including, in order from an object side, an aperture stop, a front group having positive refractive power, and a rear group having positive refractive power, in which the rear group is formed by joining a single lens having positive refractive power and a single lens having negative refractive power and is joined to an imaging device a joining surface between the single lenses has positive refractive power and the endoscope objective optical system satisfies following Conditional Expression (1):0.15
