A game apparatus includes a CPU core for creating an input envelope and a registered envelope. The input envelope has a plurality of envelope values detected from a voice waveform input in real time through a microphone. The registered envelope has a plurality of envelope values detected from a voice waveform previously input. Both of the input envelope and the registered envelope are stored in a RAM. The CPU core evaluates difference of the envelope values between the input envelope and the registered envelope. When an evaluated value satisfies a condition, the CPU core executes a process according to a command assigned to the registered envelope.