会社に限らず、入学式などもEntrance ceremony で伝えることができます。
これを使った後、 company などを使い、会社のものであることを伝えるようにするといいですね！
例：
The company's entrance ceremony is tomorrow.
その会社の入社式は明日です。
It is more common to have a "welcoming party" rather than an "Entrance ceremony".
A welcoming party is normally held in honor of the new employee to welcome them to the company and is attended by all their new colleges.
▪ Welcoming ceremony
welcoming is to new employees is to receive them with open arms and show hospitality.
a. The welcome ceremony for the new employees is next week.
▪ Welcoming ceremony（歓迎会）
これは新入社員を両手を広げて歓迎し手厚くもてなす事です。
【例文】
a. The welcome ceremony for the new employees is next week.
（新入社員歓迎会は来週行われます）
*Welcome party- It is often called a welcome party. It usually held to welcome new employees into the company and they also get a chance to meet the other people they will be working with. The plural term is welcome parties.
When someone is new and there is a party held to welcome them, then it is called:
-My colleagues hosted a welcoming party for me when I started working here.
-My colleagues and I are planning a surprise welcome party for our new boss
新人の人のためのパーティーのことを伝えるフレーズです。
-My colleagues hosted a welcoming party for me when I started working here.
私の同僚は、ここで仕事を始めたときに、私のためにウェルカムパーティーを開いてくれた。
-My colleagues and I are planning a surprise welcome party for our new boss
私の同僚と私は、新しい社長のためにサプライズでウェルカムパーティーを計画している。
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