Serial monitor display problem

In my sketch, I used Serial.begin(9600) to start serial data transmission. But, I have to set the baud rate of the serial monitor to 4800 so that I can read the output without unreadable characters. What should I go to fix this problem?

Here is my sketch.

void setup() {
  Serial.begin(9600);
  while(!Serial);
}

void loop() {
  Serial.println(9600);
  delay(1000);
}

What Arduino board and IDE are you using? It works fine for me, even as originally written: Win 7.0, Nano, 1.6.5.

You have compiled the code for 16MHz board and uploaded it to a 8MHz board I think.