The Criminal Court chief judge insists the 10-year prison sentence handed down to Voice of Taksin editor Somyot Prueksakasemsuk for lese majeste crimes is reasonable.
Mr Somyot was given a five-year jail term for each of the two charges filed against him for violating Section 112 of the Criminal Code when he published two articles deemed offensive to the monarchy in 2010.
Chief judge Thawee Prachuablarb made his comments after the European Union said it was "deeply concerned" by the court's decision on Wednesday.
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"There have been criticisms, rather one-sided, that the court was too harsh in its judgement but the five-year prison term for each of the two counts is considered appropriate," Mr Thawee said.
"It is mid-way between the minimum sentence under this law, which is three years, and the maximum punishment of 15 years. The court made its ruling in accordance with the law," he said.
The Voice of Taksin articles were not like the reform proposals aired by the Nitirat group of academics, who support an amendment to Section 112. The group's work was academic and so not held as being in breach of the law.
"The court's procedure showed the articles which Mr Somyot published did not contain academic views of the monarchy. The articles were insulting in nature and caused damage to the King," Mr Thawee said.
The sentence imposed on Mr Somyot has drawn heavy criticism from rights organisations including Freedom House and Amnesty International.
The chief judge, however, told critics to offer their opinions in good faith and without bias, or risk being prosecuted for contempt of court.
"The court's staff are monitoring the issue, especially on websites," he said.
He also said Mr Somyot's case is considered more damaging than that of red-shirt supporter Yossawaris Chuklom, alias Jeng Dokchik, who was sentenced to two years for lese majeste last month.
Mr Yossawaris was granted bail while Mr Somyot was denied bail 12 times.
"Section 112 is a crucial law involving national security. It's a law which is inviolable. The court must consider each case carefully," Mr Thawee said.
He said Mr Somyot has the right to seek bail from a higher court.