Let V be a discrete, complete, valuation ring of unequal characteristics (0
,p), and X a formal projective smooth scheme on the formal spectrum of V. L
et Z be an ample divisor on X, and U the affine open set which is the compl
ement of Z into X. In this situation, Berthelot constructed the sheaf of ar
ithmetic differential operators with overconvergent coefficients along Z, d
enoted by D dagger(co). We prove here that X is D dagger(infinity)-affine.
This result corroborates the idea that the category of coherent D dagger(in
finity)-modules can be viewed as attached to the affine open set U.