An apparatus which estimates an inside of an object, includes: a first obtaining unit which obtains light path models and a first light intensity distribution, based on an assumption that a first object includes no second object, distribution a second obtaining unit which obtains a second light intensity distribution which is an intensity distribution of observed light a voting value calculating unit which calculates a voting value for each of positions on a predetermined plane, based on a result of comparison in light intensity between the first and second light intensity distributions a voting unit which votes the voting value to voting regions on a light path model along which light reaches each position and an estimating unit which estimates whether the second object exists in each voting region, based on a result of the voting.
