how much the maximum current at the output pin arduino?
40mA source or sink current per pin, with a limit of 200mA total for the chip. But you should avoid drawing 40mA from the chip for prolonged periods, so I suggest you design for no more than 30mA continuous.
According to the datasheet, typically the output voltage of a pin will drop to 4.5V with 20mA load when using a 5V Vcc. They don't even extend the charts beyond 20mA, but it is obvious that at 40mA the output voltage of a pin would fall well below 4V. 40mA is the absolute max and should never be reached. I would recommend keeping continuous current draw to below 25mA, preferably 20mA or less on any given pin.