fortran-comment-indent-style

fortran-comment-indent-style is a variable defined in `fortran.el'.
Its value is

fixed

• This variable is safe as a file local variable if its value
  satisfies the predicate which is a byte-compiled expression.
  

Documentation:
How to indent comments.
nil forces comment lines not to be touched;
`fixed' indents to `fortran-comment-line-extra-indent' columns beyond
`fortran-minimum-statement-indent-fixed' (if `indent-tabs-mode' nil), or
`fortran-minimum-statement-indent-tab' (if `indent-tabs-mode' non-nil);
`relative' indents to current Fortran indentation plus
`fortran-comment-line-extra-indent'.

You can customize this variable.