A debugger which helps a user perform object-based debugging. A class information generation section (8) generates class information based on the source code. The execution section (12) executes the program. The object information generation section (13) generates object information based on class information and execution information. The user sets a breakpoint in a desired object via the breakpoint setting section (16). A breakpoint may be set at a desired location in the object. The break processing section (18) detects a breakpoint and breaks the execution of the program. The reservation section (21) reserves a debug operation with the identifier of an object. When there is an object that can be referenced by the reserved identifier, the reservation execution section (22) executes the operation reserved for the object.