Logstash reads the same data multiple times

Elastic Stack Logstash
1

Here is my logstash configuration that I am using on Linux system.

input
{
file{
codec => json
path => "/home/admin/ELK_Demo/demo.txt"
stat_interval => 5
start_position => "end"
}
}
filter{
json{
source=> "message"
}
}
output
{
elasticsearch
{
hosts => "localhost:9200"
}
stdout
{
codec => rubydebug
}
}

The following is the data that I am having in my log file (demo.txt) .
{ "name": "Maruti", "color": "Blue", "price": 10000, "sold": "2014-02-26"}
{ "name": "Suzuki", "color": "Red", "price": 18000, "sold": "2014-04-18"}

Whenever I am getting some new log data, the logstash is sending the same data multiple times.

Please have a look and let me know if I am doing any mistake.

Thanks!